THE  NUTRITION  OF  MAN 


THE 


NUTRITION  OF  MAN 


BY 

RUSSELL  H.  CHITTENDEN,  PH.D.,  LL.D.,  Sc.D. 

AUTHOR  OF  "PHYSIOLOGICAL  ECONOMY  IN  NUTRITION,"  ETC. 

PROFESSOR  OF  PHYSIOLOGICAL  CHEMISTRY 

AND  DIRECTOR  OF  THE  SHEFFIELD 

SCIENTIFIC    SCHOOL    OF    YALE    UNIVERSITY 


WITH    ILLUSTRATIONS 


NEW  YORK 

FREDERICK  A.  STOKES  COMPANY 
PUBLISHERS 

; 


Copyright,  1907, 
BY  FREDERICK  A.  STOKES  COMPANY 

All  rights  reserved 


May,  1907 


FIFTH  PRINTING 


PREFACE 


THE  present  book  is  the  outcome  of  a  course  of  eight  lec- 
tures delivered  before  the  Lowell  Institute  of  Boston  in  the 
early  part  of  1907. 

In  this  presentation  of  the  subject  the  attempt  has  been 
made  to  give  a  systematic  account  of  our  knowledge  regard- 
ing some  of  the  more  important  processes  of  nutrition,  with 
special  reference  to  the  needs  of  the  body  for  food.  In  doing 
this,  the  facts  accumulated  by  painstaking  observations  and 
experiments  during  recent  years  in  our  laboratory  have  been 
incorporated  with  data  from  other  sources  and  brought  into 
harmony,  so  far  as  possible,  with  the  modern  trend  of  physi- 
ological thought. 

Numerous  experimental  results,  hitherto  unpublished,  have 
been  introduced,  notably  in  Chapter  VII,  in  which  a  few  of 
the  data  recently  obtained  in  our  laboratory  with  dogs  are 
presented  in  some  detail,  since  they  afford  evidence  of  the 
error  of  the  current  arguments  concerning  the  necessity  of  a 
high  proteid  intake  by  man,  as  based  on  the  results  of  earlier 
investigators  with  high  proteid  animals. 

It  is  hoped  that  the  facts  and  arguments  here  presented 
will  help  to  arouse  a  more  general  interest  in  the  subject  of 
human  nutrition,  as  right  methods  of  living  promise  so  much 
for  the  health  and  happiness  of  the  individual  and  of  the 
community. 


CONTENTS 


CHAPTER   I  PAGE 

FOODS   AND   THEIR   DIGESTION 1 

TOPICS:  The  purpose  of  nutrition.  The  food  of  man.  Proteid  foods. 
Carbohydrate  foods.  Fats.  Food  as  fuel.  Composition  of  foodstuffs. 
Availability  of  foods.  Food  as  source  of  energy.  Various  factors  in  the 
nourishment  of  the  body.  Processes  of  digestion.  Secretion  of  saliva. 
Function  of  saliva.  Enzymes.  Reversible  action  of  enzymes.  Speci- 
ficity of  enzymes.  Mastication.  Gastric  secretion.  Components  of  gastric 
juice.  Action  of  gastric  juice.  Muscular  movements  of  stomach.  Time 
foods  remain  in  stomach.  Importance  of  stomach  digestion.  Processes 
of  the  small  intestine.  Secretion  of  pancreatic  juice.  Chemical  changes 
in  small  intestine.  Destruction  of  proteid  food.  Significance  of  the 
breaking  down  of  proteid.  Change  of  fatty  foods  and  carbohydrates  in 
intestine.  Digestion  practically  complete  at  end  of  small  intestine.  Putre- 
faction held  in  check.  Digestion  a  prelude  to  utilization  of  food. 


CHAPTER  II 

ABSORPTION,   ASSIMILATION,  AND  THE   PROCESSES  OF   METABO- 
LISM      39 

TOPICS:  Physiological  peculiarities  in  absorption.  Chemical  changes  in 
epithelial  walls  of  intestine.  Two  pathways  for  absorbed  material.  Func- 
tion of  the  liver  as  a  regulator  of  carbohydrate.  Absorption  of  proteid 
products.  Assimilation  of  food  products.  Anabolism.  Katabolism. 
Metabolism.  Processes  of  metabolism.  Older  views  regarding  oxidation. 
Discoveries  of  Lavoisier.  The  views  of  Liebig.  Theory  of  luxus  consump- 
tion. Oxidation  in  the  body  not  simple  combustion.  Oxygen  not  the 
cause  of  the  decompositions.  Oxidation  not  confined  to  any  one  place. 
Intracellular  enzymes.  Living  cells  the  guiding  power  in  katabolism. 
Some  intermediary  products  of  tissue  metabolism.  Chemical  structure  of 
different  proteids.  Decomposition  products  of  nucleoproteids.  Relation 
to  uric  acid.  Action  of  specific  intracellular  enzymes.  Creatin  and 
creatinin.  Relation  to  urea.  Proteid  katabolism  a  series  of  progressive 
chemical  decompositions.  Intracelluhir  enzymes  as  the  active  agents. 


viii  CONTENTS 

CHAPTER  in  PAGE 

THE  BALANCE  OF  NUTRITION 77 

TOPICS:  Body  equilibrium.  Nitrogen  equilibrium.  Carbon  equilibrium. 
Loss  of  nitrogen  during  fasting.  Influence  of  previous  diet  on  loss  of 
nitrogen  in  fasting.  Output  of  carbon  during  fasting.  Influence  of  pure 
proteid  diet  on  output  of  nitrogen.  Influence  of  fat  on  proteid  metabolism. 
Effect  of  carbohydrate  on  nitrogen  metabolism.  Storing  up  of  proteid  by 
the  body.  Transformation  of  energy  in  the  body.  Respiration  calorimeter. 
Basal  energy  exchange  of  the  body.  Circumstances  influencing  energy 
exchange.  Effect  of  food  on  heat  production.  Respirator}'  quotient  and 
its  significance.  Influence  of  muscle  work  on  energy  exchange.  Elimina- 
tion of  carbon  dioxide  during  work  and  with  different  diets.  Effect  of 
excessive  muscular  work  on  energy  exchange.  Oxj'gen  consumption  under 
different  conditions.  Output  of  matter  and  energy  subject  to  great  varia- 
tion. Body  equilibrium  and  approximate  nitrogen  balance  to  be  expected 
in  health. 

CHAPTER   IV 

SOURCE  OF  THE  ENERGY  OF  MUSCLE  WORK,  WITH  SOME  THEO- 
RIES OF  PROTEID  METABOLISM 119 

TOPICS:  Relation  of  muscle  work  to  energy  exchange.  Views  of  Liebig. 
Experimental  evidence.  Relation  of  nitrogen  excretion  to  muscle  work. 
Significance  of  the  respiratory  quotient  in  determining  nature  of  the  ma- 
terial oxidized.  Fats  and  carbohydrates  as  source  of  energy  by  muscles. 
Utilization  of  proteid  as  a  source  of  energy.  Formation  of  carbohydrate 
from  proteid.  Significance  of  proteid  metabolism.  Theories  of  Carl  Voit. 
Morphotic  proteid.  Circulating  proteid.  General  conception  of  proteid 
metabolism  on  the  basis  of  Voit's  theories.  Pfliiger's  views  of  proteid 
metabolism.  Rapidity  of  elimination  of  food  nitrogen.  Methods  by  which 
nitrogen  is  split  off  from  proteid.  Theories  of  Folin.  Significance  of 
creatinin  and  of  the  percentage  distribution  of  excreted  nitrogen.  Endog- 
enous or  tissue  metabolism.  Exogenous  or  intermediate  metabolism. 
Needs  of  the  body  for  proteid  food  possibly  satisfied  by  quantity  sufficient 
to  meet  the  demands  of  tissue  or  endogenous  metabolism.  Bearings  of 
Folin's  views  on  current  theories  and  general  facts  of  proteid  metabolism. 
Large  proteid  reserve  and  voluminous  exogenous  metabolism  probably  not 
needed.  Importance  of  feeding  experiments  in  determining  the  true  value 
of  different  views. 

CHAPTER  V 

DIETARY  HABITS  AND  TRUE  FOOD  REQUIREMENTS 153 

TOPICS  :  Dietetic  customs  of  mankind.  Origin  of  dietary  standards.  True 
food  requirements.  Arguments  based  on  custom  and  habit.  Relationship 


CONTENTS  ix 

PAGE 

between  food  consumption  and  prosperity.  Erroneous  ideas  regarding 
nutrition.  Commercial  success  and  national  wealth  not  the  result  of  liberal 
dietary  habits.  Instinct  and  craving  not  wise  guides  to  follow  in  choice 
and  quantity  of  food.  Physiological  requirements  and  dietary  standards 
not  to  be  based  on  habits  and  cravings.  Old-time  views  regarding  tem- 
perate use  of  food.  The  sayings  of  Thomas  Cogan.  The  teachings  of 
Cornaro.  Experimental  results  obtained  by  various  physiologists.  Work 
of  the  writer  on  true  proteid  requirements.  Studies  with  professional  men. 
Nitrogen  equilibrium  with  small  amounts  of  food.  Sample  dietaries. 
Simplicity  in  diet.  Nitrogen  requirement  per  kilogram  of  body-weight. 
Fuel  value  of  the  daily  food.  Experiments  with  University  athletes. 
Nitrogen  balance  and  food  consumption.  Sample  dietaries.  Adequacy 
of  a  simple  diet. 


CHAPTER  VI 

FURTHER  EXPERIMENTS  AND  OBSERVATIONS  BEARING  ON  TRUE 

FOOD  REQUIREMENTS 191 

TOPICS  :  Dietary  experiments  with  a  detail  of  soldiers  from  the  United 
States  Army.  General  character  of  the  army  ration.  Samples  of  the 
daily  dietary  adopted.  Rate  of  nitrogen  metabolism  attained.  Effect  on 
body-weight.  Nitrogen  balance  with  lowered  proteid  consumption.  In- 
fluence of  low  proteid  on  muscular  strength  of  soldiers  and  athletes. 
Effect  on  fatigue.  Effect  on  physical  endurance.  Fisher's  experiments 
on  endurance.  Dangers  of  underfeeding.  Dietary  observations  on  fruit- 
arians. Observations  on  Japanese  Recent  dietary  changes  in  Japanese 
army  and  navy.  Observations  of  Dr.  Hunt  on  resistance  of  low  proteid 
animals  to  poisons.  Conclusions. 


CHAPTER  VII 

THE  EFFECT  OF  Low  PROTEID  DIET  ON  HIGH  PROTEID  ANIMALS    229 

TOPICS  :  A  wide  variety  of  foods  quite  consistent  with  temperance  in  diet. 
Safety  of  low  proteid  standards  considered.  Arguments  based  on  the 
alleged  effects  of  low  proteid  diet  on  high  proteid  animals.  Experiments 
of  Immanuel  Muuk  with  dogs.  Experiments  of  Rosenheim.  Experiments 
of  Jagerroos.  Comments  on  the  above  experiments.  The  experiments  of 
Watson  and  Hunter  on  rats.  The  writer's  experiments  with  dogs.  Details 
of  the  results  obtained  with  six  dogs.  Comparison  of  the  r  suits  with 
those  of  previous  investigators.  Effect  of  a  purelv  vegetable  diet  on  dogs. 
Different  nutritive  value  of  specific  proteids  considered  Possible  influence 
of  difference  in  chemical  constitution  of  individual  proteids.  Effect  of  low 
proteid  diet  on  the  absorption  and  utilization  of  food  materials  in  the  intes- 
tine of  dogs.  General  conclusions  from  the  results  of  experiments  with 
animals. 


x  CONTENTS 

CHAPTER  VIII 

PRACTICAL  APPLICATIONS  WITH  SOME  ADDITIONAL  DATA      .     .     266 

TOPICS  :  Proper  application  of  the  results  of  scientific  research  helpful  to 
mankind.  Dietary  habits  should  be  brought  into  conformity  with  the  true 
needs  of  the  body.  The  peculiar  position  of  proteid  foods  emphasized. 
The  evil  effects  of  overeating.  What  the  new  dietary  standards  really 
involve.  The  actual  amounts  of  foodstuffs  required.  Relation  of  nutritive 
value  to  cost  of  foods.  The  advantages  of  simplicity  in  diet.  A  sample 
dietary  for  a  man  of  70  kilograms  body-weight.  A  new  method  of  indi- 
cating food  values.  Moderation  in  the  daily  dietary  leads  toward  vegetable 
foods.  The  experiments  of  Dr.  Neumann.  The  value  of  fruits  as  food. 
The  merits  of  animal  and  vegetable  proteids  considered  in  relation  to  the 
bacterial  processes  in  the  intestine.  A  notable  case  of  simplicity  in  diet. 
Intelligent  modification  of  diet  to  the  temporary  needs  of  the  body.  Diet 
in  summer  and  winter  contrasted.  Value  of  greater  protection  to  the 
kidneys.  Conclusion. 

INDEX  303 


LIST  OF  ILLUSTRATIONS 

FACING   PAGE 

Photograph  of  one  of  the  athletes 190 

Photograph  of  soldiers  taken  at  the  close  of  the  experiment      .     .     .  194 

Photograph  of  soldiers  taken  at  the  close  of  the  experiment      .     .     .  195 

Photograph  of  Fritz  at  the  close  of  the  experiment 200 

Photographs  of  the  dogs  experimented  with 

Subject  No.  5  August  19,  1905 246 

Subject  No.  5  November  18,  1905 246 

Subject  No.  5  April  24,  1906 247 

Subject  No.  5  June  27,  1906 247 

Subject  No.  3  August  19,  1905 248 

Subject  No.  3  November  18,  1905 248 

Subject  No.  3  April  24,  1906 249 

Subject  No.  3  June  27,  1906 249 

Subject  No.  13  January  2,  1906 250 

Subject  No.  13  February  27,  1906 250 

Subject  No.  13  April  24,  1906 251 

Subject  No.  13  June  19,  1906 251 

Subject  No.  15  January  2,  1906 252 

Subject  No.  15  February  27,  1906 252 

Subject  No.  15  April  24,  1906 253 

Subject  No.  15  June  19,  1906 253 

Subject  No.  20  January  2,  1906 254 

Subject  No.  20  February  27,  1906 254 

Subject  No.  20  April  24,  1906 2;,5 

Subject  No.  20  June  19,  1906 255 

Subject  No.  17  January  2,  1906 256 

Subject  No.  17  February  27,  1906 256 

Subject  No.  17  April  24,  1906 257 

Subject  No.  17  June  27,  1906 257 


THE  NUTRITION  OF  MAN 

CHAPTER  I 
FOODS  AND  THEIR  DIGESTION 

TOPICS  :  The  purpose  of  nutrition.  The  food  of  man.  Proteid  foods. 
Carbohydrate  foods.  Fats.  Food  as  fuel.  Composition  of  foodstuffs. 
Availability  of  foods.  Food  as  source  of  energy.  Various  factors  in 
the  nourishment  of  the  body.  Processes  of  digestion.  Secretion  of 
saliva.  Function  of  saliva.  Enzymes.  Reversible  action  of  enzymes. 
Specificity  of  enzymes.  Mastication.  Gastric  secretion.  Components 
of  gastric  juice.  Action  of  gastric  juice.  Muscular  movements  of 
stomach.  Time  foods  remain  in  stomach.  Importance  of  stomach 
digestion.  Processes  of  the  small  intestine.  Secretion  of  pancreatic 
juice.  Chemical  changes  in  small  intestine.  Destruction  of  proteid 
food.  Significance  of  the  breaking  down  of  proteid.  Change  of  fatty 
foods  and  carbohydrates  in  intestine.  Digestion  practically  complete 
at  end  of  small  intestine.  Putrefaction  held  in  check.  Digestion 
a  prelude  to  utilization  of  food. 

ONE  of  the  great  mysteries  of  life  is  the  power  of  growth, 
that  harmonious  development  of  composite  organs  and 
tissues  from  simple  protoplasmic  cells,  with  the  ultimate 
formation  of  a  complex  organism  with  its  orderly  adjustment 
of  structure  and  function.  Equally  mysterious  is  that  won- 
derful power  of  rehabilitation  by  which  the  cells  of  the  body 
are  able  to  renew  their  living  substance  and  to  maintain 
their  ceaseless  activity  through  a  period,  it  may  be  of  four- 
score years,  before  succumbing  to  the  inevitable  fate  that 
awaits  all  organic  structures.  This  bodily  activity,  visible 
and  invisible,  is  the  result  of  a  third  mysterious  process, 
more  or  less  continuous  as  long  as  life  endures,  of  chemical 


i:  THE  NUTRITION   OF  MAN 

disintegration,  decomposition,  and  oxidation,  by  which  arises 
the  evolution  of  energy  to  maintain  the  heat  of  the  body  and 
the  power  for  mental  and  physical  work. 

These  three  main  functions  constitute  the  purpose  of  nutri- 
tion. The  growth  of  the  adult  man  from  the  tiny  cell  or 
germ  that  marks  his  simple  beginning  is  at  the  expense  of 
the  food  material  he  absorbs  and  assimilates.  The  rehabili- 
tation of  the  cells,  or  the  composite  tissues  of  the  fully  de- 
veloped organism,  is  accomplished  through  utilization  of  the 
daily  food,  whereby  cell  substance  is  renewed  and  all  losses 
made  good.  The  energy  which  manifests  itself  in  the  form 
of  heat  and  mechanical  or  mental  work,  i.  e.,  the  energy  by 
which  the  vital  machinery  is  maintained  in  ceaseless  activity, 
comes  from  the  breaking  down  of  the  food  materials  by  means 
of  which,  as  the  saying  goes,  the  body  is  nourished.  The 
body  thus  becomes  the  centre  of  different  lines  of  activity, 
the  food  serving  as  the  material  out  of  which  new  cells  and 
tissues  are  constructed,  old  cells  revivified,  and  energy  for 
running  the  bodily  machinery  derived.  Development,  growth, 
and  vital  activity  all  depend  upon  the  availability  of  food 
in  proper  amounts  and  proper  quality. 

The  food  of  man  is  composed  mainly  of  organic  materials, 
for  while,  as  Dr.  Curtis  1  has  expressed  it,  "  the  plant  can 
make  organic  matter  out  of  inorganic  elements,  just  this  the 
animal  cannot  do  at  all.  The  thing  of  legs  and  locomotion, 
of  spine  and  speech,  can  build  his  organic  walls  only  out  of 
organic  bricks  ruthlessly  ripped  from  existing  walls  of  other 
animals  or  plants."  It  is  true  that  man  has  need  of  certain 
inorganic  salts  in  his  daily  diet,  but  they  are  in  the  nature 
of  aids  to  nutrition  (aside  from  such  as  are  necessary  for  the 
formation  of  bone  and  teeth),  contributing  in  some  measure 
toward  regulation  and  control  of  nutritive  processes  rather 

1  Edward  Curtis,  M.D.  Nature  and  Health  :  Henry  Holt  &  Co.,  New  York. 
/906.  p.  39. 


FOODS   AND  THEIK   DIGESTION  3 

than  as  a  source  of  energy  to  the  body.  Inorganic  substances, 
however,  are  an  integral  part  of  the  essential  tissues  and 
organs  of  the  body,  being  combined  with  the  organic  con- 
stituents of  the  living  cells.  Indeed,  electrolytes  are  perhaps 
the  substances  that  put  life  into  the  proteids  of  the  protoplasm, 
and  it  is  truly  important  for  the  integrity  and  functional 
power  of  living  cells  that  the  proportion  of  inorganic  con- 
stituents therein  be  kept  in  a  constant  condition  of  quality 
and  quantity.  Still,  the  food  of  mankind  is  essentially  or- 
ganic in  nature,  and  while  it  may  be  exceedingly  varied  in 
character,  ranging  from  the  simple  vegetable  dietary  of  the 
natives  of  India  and  the  Far  East  to  the  voluminous  admix- 
ture of  varied  forms  of  animal  and  vegetable  foodstuffs  so 
acceptable  to  the  Ion  vivant  of  our  western  civilization,  the 
principles  contained  therein  are  few  in  number. 

The  organic  foodstuffs  are  of  three  distinct  types  and  are 
classified  under  three  heads,  viz. :  Proteids  or  Albuminous 
foodstuffs,  Carbohydrates,  and  Fats.  All  animal  and  vege- 
table foods,  whatever  their  nature  and  whatever  their  origin, 
are  composed  "simply  of  representatives  of  one  or  more  of 
these  three  classes  of  food  principles. 

Proteid  substances  are  characterized  by  containing  about 
16  per  cent  of  nitrogen.  In  addition,  they  contain  on  an 
average  52  per  cent  of  carbon,  7  per  cent  of  hydrogen,  23 
per  cent  of  oxygen,  and  0.5-2.0  per  cent  of  sulphur.  A 
certain  class  of  proteids,  known  as  nucleoproteids  because 
of  their  occurrence  in  the  nuclei  of  cells,  contain  likewise  a 
small  amount  of  phosphorus  in  organic  combination.  Pro- 
teid or  albuminous  substances  constitute  the  chemical  basis 
of  all  living  cells,  whether  animal  or  vegetable.  This  means, 
expressed  in  different  language,  that  the  organic  substance 
of  all  organs  and  tissues,  whether  of  animals  or  plants,  is 
made  up  principally  of  proteid  matter.  Proteid  substances 
occupy,  therefore,  a  peculiar  position  in  the  nutrition  of  man 


4  THE  NUTRITION  OF  MAN 

and  of  animals  in  general.  They  constitute  the  class  of  essen- 
tial foodstuffs  without  which  life  is  impossible.  For  tissue- 
building  and  for  the  renewal  of  tissues  and  organs,  or  their 
component  cells,  proteid  or  albuminous  foodstuffs  are  an 
absolute  requirement.  The  vital  part  of  all  tissue  is  proteid, 
and  only  proteid  food  can  serve  for  its  growth  or  renewal. 
Hence,  no  matter  how  generous  the  supply  of  carbohydrates 
and  fats,  without  some  admixture  of  proteid  food  the  body 
will  weaken  and  undergo  "nitrogen  starvation."  It  is  to  be 
noted,  however,  that  while  the  element  nitrogen  (16  per 
cent)  gives  character  to  the  proteid  or  albuminous  foodstuffs, 
so  that  they  are  frequently  spoken  of  or  classified  as  the 
"nitrogenous  foodstuffs,"  it  is  not  the  nitrogen  per  se  that  is 
so  essential  for  the  nutrition  of  the  body.  Man  lives  in  an  at- 
mosphere of  oxygen  and  nitrogen.  He  can  and  does  absorb 
and  utilize  the  free  oxygen  of  the  air  he  breathes;  indeed,  it 
is  absolutely  essential  for  his  existence,  but  the  free  nitrogen 
likewise  drawn  into  the  lungs  at  each  inspiration  is  of  no 
avail  for  the  needs  of  the  body.  Further,  there  are  many 
compounds  of  nitrogen,  some  of  them  closely  allied  to  the 
proteid  foodstuffs  in  chemical  composition,  which  are  just 
as  useless  as  free  nitrogen  in  meeting  the  wants  of  the  body 
for  nitrogenous  foods. 

Dame  Nature  is  very  discriminating;  she  demands  a  defi- 
nite form  of  nitrogenous  compound,  some  peculiar  or  specific 
grouping  of  the  nitrogen  element  with  other  elements  in  the 
food  that  can  make  good  the  waste  of  proteid  tissue.  In  the 
inactive  and  fibrous  tissues  of  animals,  such  as*  are  found  in 
bones,  tendons,  and  ligaments,  there  is  present  a  substance 
known  as  collagen,  which,  when  boiled  with  water,  as  in  the 
making  of  soups,  is  transformed  into  gelatin.  This  body, 
because  of  its  close  chemical  relationship  to  proteid  or  albu- 
minous substances,  is  known  as  an  albuminoid.  Yet,  though 
it  has  essentially  the  same  chemical  composition  as  ordinary 


FOODS  AND  THEIK  DIGESTION  5 

albuminous  substances  and  shows  many  of  the  reactions  char- 
acteristic of  the  latter,  it  cannot  take  the  place  of  true  pro- 
teid  in  building  up  or  repairing  the  tissues  of  the  body.  To 
quote  again  from  Dr.  Curtis:  "Tissue  is  nitrogenous,  so 
that,  of  course,  only  nitrogenous  food  can  serve  for  its  mak- 
ing ;  but  of  the  two  kinds  of  nitrogenous  principles,  proteids 
and  albuminoids,  behold,  proteids  only  are  of  avail!  Why 
this  is  so  is  unknown,  since  albuminoid  is  equally  nitroge- 
nous with  proteid;  but  so  it  is  —  proteid  and  proteid  alone 
can  fulfil  the  high  function  of  furnishing  the  material  basis 
of  life.  Gelatin  cannot  even  go  to  make  the  very  kind  of 
tissue  of  which  itself  is  a  derivative.  Alongside  of  its 
brother  proteid,  gelatin  stands  as  a  prince  of  the  blood  whose 
escutcheon  bears  the  '  bend  sinister.'  Such  a  one,  though  of 
royal  lineage,  may  never  aspire  to  the  throne."  It  is  thus 
quite  clear  that  the  true  proteid  foods  are  tissue  builders  in 
the  broadest  sense  of  the  term,  and  it  is  equally  evident  that 
they  are  absolutely  essential  for  life,  since  no  other  kind  or 
form  of  foodstuff  can  take  their  place  in  supplying  the  needs 
of  the  body.  Every  living  cell,  whether  of  heart,  muscle, 
brain,  or  nerve,  requires  its  due  allowance  of  proteid  material 
to  maintain  its  physiological  rhythm.  No  other  foodstuff 
stands  in  such  intimate  relationship  to  the  vital  processes, 
but  so  far  as  we  know  at  present  any  form  of  true  proteid, 
whether  animal  or  vegetable,  will  serve  the  purpose. 

Carbohydrates  include  two  closely  related  classes  of  com- 
pounds, viz.,  sugars  and  starches.  They  are  entirely  free 
from  nitrogen,  containing  only  carbon  (44.4  per  cent),  hydro- 
gen (6.2  per  cent),  and  oxygen  (49.4  per  cent),  and  hence  are 
classified  as  non-nitrogenous  foods.  Obviously,  they  cannot 
serve  as  tissue  builders,  but  by  oxidation  they  yield  energy 
for  heat  and  work.  They  constitute  an  easily  oxidizable 
form  of  fuel,  and  when  supplied  in  undue  amounts  they 
may  undergo  transformation  within  the  body  into  fat,  which 


6  THE  NUTRITION  OF  MAN 

is  temporarily  deposited  in  tissues  and  organs  for  future 
needs. 

Fats,  like  carbohydrates,  are  free  from  nitrogen,  but  differ 
from  them  in  containing  a  much  larger  percentage  of  carbon, 
and  hence  have  greater  fuel  value  per  pound.  Fats  contain 
on  an  average  76.5  per  cent  of  carbon,  11.9  per  cent  of 
hydrogen,  and  11.5  per  cent  of  oxygen.  With  their  larger 
content  of  carbon  and  smaller  proportion  of  oxygen,  fats  are 
less  easily  oxidizable  than  sugars,  requiring  a  larger  intake 
of  oxygen  for  their  combustion,  but  when  oxidized  they  yield 
more  heat  per  pound  than  carbohydrates. 

Fats  and  carbohydrates  are  thus  seen  to  be  the  natural  fuel 
foodstuffs  of  the  body.  They  cannot  serve  for  the  upbuild- 
ing or  renewal  of  tissue,  but  by  oxidation  they  constitute  an 
economical  fuel  for  maintaining  body  temperature  and  for 
power  to  run  the  bodily  machinery.  It  should  be  remem- 
bered, however,  that  anything  capable  of  being  burned  in 
the  body  may  serve  as  fuel  material;  hence  proteid  food, 
though  of  specific  value  as  a  tissue  builder,  may  likewise  by 
its  oxidation  yield  energy  for  heat  and  work,  but  its  combus- 
tion, owing  to  the  content  of  nitrogen,  is  never  complete. 
Further,  its  use  as  fuel  is  uneconomical  and  undesirable  for 
reasons  to  be  discussed  later,  but  it  is  well  to  know  that  its 
oxidation,  though  incomplete,  is  accompanied  by  the  libera- 
tion of  energy,  as  in  the  oxidation  of  non-nitrogenous  foods. 
A  portion  of  the  carbon,  hydrogen,  and  oxygen  of  the  proteid 
molecule  will  burn  within  the  body  to  gaseous  products,  as 
do  sugars  and  fats,  but  there  remains  a  nucleus  of  nitrogen, 
with  some  carbon,  hydrogen,  and  oxygen,  which  resists  com- 
bustion and  must  be  gotten  rid  of  by  the  combined  labors  of 
liver  and  kidneys.  Fats  and  carbohydrates,  on  the  other 
hand,  undergo  complete  combustion  to  simple  gaseous  prod- 
ucts, carbon  dioxide  and  water,  which  are  easily  removed  by 
the  lungs,  skin,  etc. 


FOODS   AND  THEIR  DIGESTION  7 

These  three  classes  of  foodstuffs  exist  in  a  great  variety 
of  combinations  or  admixtures  in  nature.  In  many  cases, 
noticeably  in  milk,  all  three  occur  together  in  fairly  large 
quantities.  In  animal  foods,  such  as  meats,  fish,  etc.,  pro- 
teid  and  fat  alone  are  found,  while  in  perfectly  lean  meat 
proteid  only  is  present,  excepting  a  small  amount  of  fat. 
Again,  the  white  of  the  egg  contains  proteid  alone.  Hence, 
a  meat  and  egg  diet  would  be  essentially  a  proteid  diet.  In 
vegetable  foods,  as  in  the  cereals,  there  is  found  an  admix- 
ture of  proteid  and  starch,  the  latter  predominating  in  many 
cases,  as  in  wheat  flour.  The  following  table,1  showing  the 
chemical  composition  of  various  food  materials,  may  be  of 
service  in  throwing  light  on  the  relative  distribution  of  the 
three  classes  of  foodstuffs  in  natural  products. 


THE   CHEMICAL  COMPOSITION  OF  SOME  COMMON  FOOD 
MATERIALS 


Food  Materials. 

Proteid. 

Carbo- 
hydrate. 

Fat. 

Water. 

Mineral 
Matter. 

Fuel  Value 
per  pound. 

Fresh  beef,  loin,  lean,  edi- 
ble portion      

per  cent 
24.2 

per  cent 
0 

per  cent 
3.7 

per  cent 
70.8 

per  cent 

1.3 

calories 
615 

Fresh    beef,    round,   lean, 

edible  portion     .... 

22.3 

0 

2.8 

73.6 

1.3 

540 

Fresh  Porterhouse    steak, 

edible  portion     .... 

21.9 

0 

20.4 

60.0 

1.0 

1270 

Fresh  beef  liver    .... 

21.0 

1.7 

4.5 

71.2 

1.6 

605 

Fresh  beef  tongue     .    .    . 

19.0 

0 

9.2 

70.8 

1.0 

740 

Fresh  sweetbreads     .     .     . 

16.8 

0 

12.1 

70.9 

1.6 

825 

Fresh  beef  kidney     .    .    . 

16.9 

.0.4 

4.8 

76.7 

1.2 

520 

Cooked  beef,  roasted     .    . 

22.3 

0 

28.6 

48.2 

1.3 

1620 

Cooked  round  steak  .     . 

27.6 

0 

7.7 

63.0 

1.8 

840 

1  The  data  composing  this  table  are  taken  from  Bulletin  28  (Revised 
Edition),  United  States  Department  of  Agriculture,  Office  of  Experiment 
Stations. 


THE  NUTKITION  OF  MAN 


THE  CHEMICAL  COMPOSITION  OF  SOME  COMMON  FOOD 
MATERIALS 


Pood  Materials. 

Proteid. 

Carbo- 
hydrate. 

Pat. 

Water. 

Mineral 
Matter. 

Fuel  Value 
per  pound. 

per  cent 

per  cent 

per  cent 

per  cent 

per  cent 

calories 

Broiled  tenderloin  steak    . 

23.5 

0 

20.4 

64.8 

1.2 

1300 

Dried  beef,  canned    .    .    . 

39.2 

0 

5.4 

44.8 

11.2 

960 

Stewed  kidneys,  canned     . 

18.4 

2.1 

5.1 

71.9 

2.5 

600 

Fresh  corned  beef,  edible 

15.3 

o 

26.2 

53.6 

4.9 

IOQK 

Fresh  breast  of  veal,  lean  . 

21.2 

0 

8.0 

70.3 

1.0 

&OvU 

730 

Fresh  leg  of  lamb,  edible 

portion                .    .    .    . 

19.2 

o 

16.5 

63.9 

1.1 

1AKK 

1UOO 

Lamb  chops,  broiled      .    . 

21.7 

0 

29.9 

47.6 

1.3 

1665 

Roast  leg  of  lamb,  edible 

portion  

19.4 

o 

12.7 

67.1 

0.8 

900 

Roast  leg  of  mutton,  edible 

25.9 

o 

22.6 

50.9 

1.2 

1420 

Fresh  lean  ham    .... 

25.0 

0 

14.4 

60.0 

1.3 

J.*t^V 

1075 

Smoked    ham,   fat,  edible 

portion       • 

14.8 

o 

52.3 

27.9 

3.7 

O4Q  K 

Chicken,    broilers,    edible 

AVOU 

portion       

21.6 

o 

2.6 

74.8 

1.1 

Kf)K 

Turkey,  edible  portion  .    . 

21.1 

0 

22.9 

55.5 

1.0 

OUt/ 

1360 

Roast  turkey,  edible  por- 

tion     

27.8 

0 

18.4 

52.0 

1.2 

1295 

Fricasseed  chicken,  edible 

portion            .         . 

17.6 

2.4 

11.5 

67.5 

1.0 

OKK 

Fresh  cod,  dressed     .    .    . 

11.1 

0 

0.2 

58.5 

0.8 

ooo 
215 

Fresh  mackerel,  edible  por- 

tion   

18.7 

o 

7.1 

73.4 

1.2 

645 

Fresh  halibut,  steaks     .    . 

18.6 

0 

6.2 

75.4 

1.0 

565 

Fresh  shad,  edible  portion 

18.8 

0 

9.5 

70.6 

1.3 

750 

Fresh  smelt,  edible  portion 

17.6 

0 

1.8 

79.2 

1.7 

405 

Cooked      bluefish,    edible 

portion  

26.1 

o 

4.5 

68.2 

1.2 

670 

Broiled  Spanish  mackerel, 

edible  portion     .... 

23.2 

0 

6.5 

68.9 

1.4 

715 

FOODS  AND  THEIR  DIGESTION 


9 


THE  CHEMICAL  COMPOSITION  OF  SOME  COMMON  FOOD 
MATERIALS 


Food  Materials. 

Proteid. 

Carbo- 
lydrate. 

Pat. 

Water. 

Mineral 
Matter. 

Fuel  Value 
per  pound. 

Salt    codfish,    edible    por- 
tion .              . 

>er  cent 

25.4 

per  cent 

o 

per  cent 
03 

per  cent 
53.5 

per  cent 

24.7 

calories 
410 

Salt  mackerel,  edible  por- 
tion     

220 

o 

22.6 

42.2 

13.2 

1345 

Canned  salmon,  edible  por- 

21.8 

o 

12.1 

63.5 

2.6 

915 

Canned     sardines,    edible 
portion                 .     •         . 

230 

o 

197 

523 

5.6 

162 

Fresh  round  clams     .    .    . 
Fresh  oysters,  solid   .    .    . 
Fresh  hen's  eggs   .... 
Boiled  hen's  eggs  .... 
Butter  

6.5 
6.0 
13.4 
13.2 
1.0 

4.2 
3.3 
0 
0 
0 

0.4 
1.3 
10.5 
12.0 
85.0 

86.2 
88.3 
73,7 
73.2 
11.0 

2.7 
1.1 
1.0 
0.8 
3.0 

215 
230 

720 
765 
3605 

Full  cream  cheese     .    .    . 
Whole  cow's  milk      .    .    . 
Corn  meal,  unbolted      .    . 
Oatmeal  .    .         .         .    . 

25.9 
3.3 
8.4 
161 

2.4 
5.0 
74.0 
675 

33.7 
4.0 

4.7 

72 

34.2 
87.0 
11.6 
73 

3.8 
0.7 
1.3 
1  9 

1950 
325 
1730 
1860 

Rice     

8.0 

790 

0.3 

123 

04 

1630 

Wheat  flour,  entire  wheat 

13.8 

2.8 

71.9 
244 

1.9 
0.1 

11.4 
72.5 

1.0 

0.2 

1675 
525 

Shredded  wheat    .... 
Macaroni       .         .... 

10.5 
134 

77.9 
741 

1.4 

09 

8.1 
103 

2.1 
13 

1700 
1665 

5.4 

47.1 

1.8 

43.6 

2.1 

1050 

Wheat  bread  or  rolls     .    . 
Whole  wheat  bread  .    .    . 

8.9 
9.4 
9.8 

56.7 
497 
73.1 

4.1 
0.9 
9.1 

29.2 
38.4 
5.9 

1.1 
1.3 
2.1 

1395 
1140 
1925 

Oyster  crackers     .... 

11.3 
5.8 

,  70.5 
635 

10.5 
90 

4.8 
188 

2.9 
29 

1965 
1670 

Sponge  cake     

63 

659 

107 

153 

1  8 

1795 

88 

70.6 

5.0 

150 

06 

1685 

31 

42.8 

98 

425 

18 

1270 

4.2 

26.1 

6.3 

62.4 

1.0 

830 

4.4 

21.7 

8.4 

642 

1  3 

840 

10 


THE  NUTBITION  OF 


THE  CHEMICAL  COMPOSITION  OF   SOME  COMMON  FOOD 
MATERIALS 


Food  Materials. 

Proteid. 

Carbo- 
hydrate 

Fat. 

Water. 

Mineral 
Matter. 

Fuel  Value 
per  pound 

per  cent 

per  cent 

per  cent 

per  cent 

per  cent 

calories 

Indian  meal  pudding      .    . 

5.5 

27.5 

4.8 

60.7 

1.5 

815 

Tapioca  pudding  .... 

3.3 

28.2 

3.2 

64.5 

0.8 

720 

Fresh  asparagus    .... 

1.8 

3.3 

0.2 

94.0 

0.7 

105 

Fresh  lima  beans  .... 

7.1 

22.0 

0.7 

68.5 

1.7 

570 

Dried  lima  beans  .... 

18.1 

65.9 

1.5 

10.4 

4.1 

1625 

22.5 

59.6 

1.8 

12.6 

3.5 

1605 

Cooked  beets         . 

2.3 

7.4 

0.1 

88.6 

1.6 

185 

Fresh  cabbage,  edible  por- 

1.6 

5.6 

0.3 

91.5 

1.0 

145 

Green  corn,  edible  portion 

3.1 

19.7 

1.1 

75.4 

0.7 

470 

24.6 

62.0 

1.0 

9.5 

2.9 

1655 

Green  peas  

7.7 

16.9 

0.5 

74.6 

1.0 

465 

Raw  potatoes,  edible  portion 

2.2 

18.4 

0.1 

78.3 

1.0 

385 

Boiled  potatoes     .... 

2.5 

20.9 

01 

75.5 

1.0 

440 

Fresh  tomatoes     .... 

0.9 

3.9 

0.4 

94.3 

0.5 

105 

Baked  beans,  canned     .    . 

6.9 

19.6 

2.5 

68.9 

2.1 

600 

Apples,  edible  portion  .     . 

0.4 

14.2 

0.5 

84.6 

3.0 

290 

Bananas,  yellow,  edible  por- 

tion                     . 

1.3 

22.0 

0.6 

75.3 

0.8 

460 

Fresh  cranberries  .... 

0.4 

9.9 

0.6 

88.9 

0.2 

215 

Oranges,  edible  portion  .     . 

0.8 

11.6 

0.2 

86.9 

0.5 

240 

Peaches,  edible  portion  .     . 

0.7 

9.4 

0.1 

89.4 

0.4 

190 

Fresh  strawberries     .    .     . 

1.0 

7.4 

0.6 

90.4 

0.6 

180 

Dried  prunes,  edible  portion 

2.1 

73.3 

0.0 

22.3 

2.3 

1400 

Almonds,  edible  portion      . 

21.0 

17.3 

54.9 

4.8 

2.0 

3030 

Peanuts,  edible  portion  .     . 

25.8 

24.4 

38.6 

9.2 

2.0 

2560 

Pine  nuts,  edible  portion    . 

33.9 

6.9 

49.4 

6.4 

3.4 

2845 

Brazil  nuts,  edible  portion  . 

17.0 

7.0 

66.8 

5.3 

3.9 

3265 

Soft-shell    walnuts,    edible 

16.6 

16.1 

63.4 

2.5 

1.4 

3285 

FOODS  AND  THEIR  DIGESTION  11 

In  commenting  on  these  figures,  reference  to  which  will  be 
made  from  time  to  time  in  other  connections,  it  may  be  wise 
to  emphasize  the  large  amount  of  water  almost  invariably 
present  in  natural  foodstuffs.  Further,  it  is  to  be  noted  that, 
in  animal  products  especially,  the  variations  in  proteid-content 
are  in  large  measure  coincident  with  variations  in  the  amount 
of  water  present.  In  other  words,  foods  of  animal  origin  if 
freed  entirely  of  water  would,  as  a  rule,  show  essentially  the 
same  percentage  of  proteid  matter.  Fat  is  naturally  variable, 
according  to  the  condition  of  the  animal  at  the  time  it  was 
slaughtered.  Among  the  vegetable  products,  carbohydrate, 
mainly  in  the  form  of  starch,  becomes  exceedingly  con- 
spicuous, though  proteid  is  by  no  means  lacking.  Indeed, 
in  some  cereals,  as  in  oatmeal,  in  dried  peas  and  beans,  the 
content  of  proteid  will  average  as  high  as  in  fresh  beef,  while 
in  addition  50-70  per  cent  of  the  entire  substance  is  made  up 
of  carbohydrate.  Again,  in  the  edible  nuts,  the  content  of 
proteid  runs  high,  in  some  cases  higher  than  in  fresh  beef, 
while  at  the  same  time  carbohydrate  and  fat  are  noticeably 
large.  Further,  it  is  to  be  noted  that  in  nuts  there  is  here 
and  there  some  striking  individuality,  as  in  pine  nuts  and 
Brazil  nuts,  both  of  which  show  a  noticeable  lack  of  carbo- 
hydrate as  contrasted  with  peanuts,  almonds,  and  walnuts; 
a  fact  of  some  importance  in  cases  where  a  vegetable  food 
rich  in  proteid  is  desired,  but  with  freedom  from  starch. 

Another  generality,  to  be  thoroughly  understood,  is  that 
while  the  figures  given  for  proteid  express  quite  clearly  and 
with  reasonable  degree  of  accuracy  the  relative  amounts  of 
proteid  matter  present  in  the  foodstuffs  in  question,  there 
may  be  important  differences  in  availability  of  which  the 
percentage  figures  give  no  suggestion.  In  other  words,  the 
analytical  data  deal  solely  with  the  total  content  of  proteid, 
while  there  is  needed  in  addition  information  as  to  the  rela- 
tive digestibility,  or  availability  by  the  body,  of  the  different 


12  THE  NUTRITION  OF  MAN 

kinds  of  proteid  food.  For  example,  roast  mutton,  cream 
cheese,  and  dried  peas  contain  approximately  the  same 
amount  of  proteid.  Are  we  then  to  infer  that  these  three 
foods  have  the  same  nutritive  value  so  far  as  proteid  is  con- 
cerned? Surely  not,  since  no  account  is  taken  of  the  rela- 
tive digestibility  of  the  three  foods.  It  is  one  of  the  axioms 
of  physiology  that  the  true  nutritive  value  of  any  proteid 
food  is  dependent  not  alone  upon  the  amount  of  proteid  con- 
tained therein,  but  upon  the  quantity  of  proteid  that  can  be 
digested  and  absorbed ;  or,  in  other  words,  made  available  for 
the  needs  of  the  body.  The  same  rule  holds  good  for  both 
fats  and  carbohydrates,  but  as  proteid  is  the  more  im- 
portant foodstuff,  and  is  as  a  rule  taken  more  sparingly,  the 
question  of  availability  has  greater  import  with  the  proteid 
foods. 

The  availability  or  digestibility  of  foods  can  be  determined 
only  by  physiological  experiment.  By  making  a  comparison 
for  a  definite  period  of  time  of  the  amount  of  a  given  food  in- 
gredient consumed  and  the  amount  that  passes  unchanged 
through  the  intestine,  an  estimate  of  its  digestibility  can  be 
made.  The  result,  to  be  sure,  is  not  wholly  free  from  error, 
since  we  cannot  always  distinguish  between  the  undigested 
food  and  so-called  metabolic  products  coming  from  the  diges- 
tive juices  and  from  the  walls  of  the  intestine ;  but  the  errors 
are  not  large,  and  results  so  obtained  are  full  of  meaning. 
In  a  general  way  it  may  be  stated  that  with  animal  foods, 
such  as  meats,  eggs,  and  milk,  about  97  per  cent  of  the  con- 
tained proteid  is  digested  and  thereby  rendered  available  for 
the  body.  With  ordinary  vegetable  foods,  on  the  other  hand, 
as  they  are  usually  prepared  for  consumption,  only  about 
85  per  cent  of  the  proteid  is  made  available.  This  is  par- 
tially due  to  the  presence  in  the  vegetable  tissue  of  cellulose, 
which  in  some  measure  prevents  that  thorough  attack  of  the 
proteid  by  the  digestive  juices  which  occurs  with  animal 


FOODS  AND  THEIR  DIGESTION  13 

foods.  With  a  mixed  diet,  i.  e.,  with  a  variable  admixture 
of  animal  and  vegetable  foods,  it  is  usually  considered  that 
about  92  per  cent  of  the  proteid  contained  therein  will  un- 
dergo digestion. 

Regarding  differences  in  the  availability  of  fats,  it  may  be 
stated  that,  as  a  rule,  the  fatty  matter  contained  in  vegetable 
foods  is  less  readily,  or  less  thoroughly,  digested  than  that 
present  in  foods  of  animal  origin.  In  the  latter,  about  95 
per  cent  of  the  fat  is  digested  and  absorbed.  This  figure, 
however,  is  generally  taken  as  representing  approximately  the 
digestibility  or  availability  of  the  fat  contained  in  man's  daily 
dietary,  since  by  far  the  larger  proportion  of  the  fat  consumed 
is  of  animal  origin.  Carbohydrates,  on  the  other  hand,  are 
much  more  easily  utilized  by  the  body.  Naturally,  sugars, 
owing  to  their  great  solubility  and  ready  diffusibility,  offer 
little  difficulty  in  the  way  of  easy  digestion;  but  starches 
likewise,  though  not  so  readily  assimilable,  are  digested,  as 
a  rule,  to  the  extent  of  98  per  cent  or  more  of  the  amount 
consumed.  It  is  thus  evident  that  in  any  estimate  of  the 
food  value  of  a  given  diet,  chemical  composition  is  to 
be  checked  by  the  digestibility  or  availability  of  the  food 
ingredients. 

As  has  been  stated  several  times,  the  proteid  foodstuffs 
are  the  more  important,  since  proteid  matter  is  essential  to 
animal  life.  Man  must  have  a  certain  amount  of  proteid 
food  to  maintain  the  body  in  a  condition  of  strength  and 
vigor.  The  other  essential  is  that  the  daily  food  furnish 
sufficient  energy  to  meet  the  needs  of  the  body  for  heat  and 
power.  This  means  that  in  addition  to  proteid,  which  pri- 
marily serves  a  particular  purpose,  there  must  be  enough 
non-nitrogenous  food  (either  carbohydrate  or  fat  or  both)  to 
provide  the  requisite  fuel  for  oxidation  or  combustion  to 
meet  the  demands  of  the  body  for  heat  and  for  work ;  both 
of  which  are  subject  to  great  variation  owing  to  differences 


14  THE  NUTRITION   OF  MAN 

in  the  temperature  of  the  surrounding  air,  and  especially  be- 
cause of  variations  in  the  degree  of  bodily  activity.  The 
energy  which  a  given  foodstuff  will  yield  can  be  ascertained 
by  laboratory  experiment,  in  which  a  definite  weight  of  the 
substance  is  burned  or  oxidized  in  a  calorimetric  bomb  under 
conditions  where  the  exact  amount  of  heat  liberated  can  be 
accurately  measured.  The  fuel,  or  energy,  value  so  obtained 
is  expressed  in  calories  or  heat  units.  A  calorie  may  be  de- 
fined as  the  amount  of  heat  required  to  raise  1  gram  of  water 
I3  C.,  or,  to  be  more  exact,  the  amount  of  heat  required  to 
raise  1  gram  of  water  from  15°  to  16°  C.  This  unit  is 
usually  spoken  of  as  the  small  calorie,  to  distinguish  it 
from  the  large  calorie,  which  represents  the  amount  of  heat 
required  to  raise  1  kilogram  of  water  1°  C.  Hence,  the 
large  calorie  is  equal  to  one  thousand  small  calories.  When 
burned  in  a  calorimeter,  1  gram  of  carbohydrate  yields  on 
an  average  4100  gram-degree  units  of  heat,  or  small  calories; 
1  gram  of  fat  yields  9300  small  calories.  Both  of  these  non- 
nitrogenous  foods  burn  or  oxidize  to  the  same  products  - 
viz.,  carbon  dioxide  and  water  —  when  utilized  in  the  body 
as  when  burned  in  the  calorimeter;  hence,  the  figures  given 
represent  the  physiological  heat  of  combustion,  per  gram,  of 
the  two  classes  of  foodstuffs.  Obviously,  the  fuel  values  of 
different  foods  belonging  to  the  same  group  or  class  will 
show  slight  variation,  but  the  above  figures  represent  average 
values. 

Unlike  fats  and  carbohydrates,  proteids  are  not  burned 
completely  in  the  body;  hence,  the  physiological  fuel  value 
of  a  proteid  is  less  than  the  value  obtained  by  oxidation  in 
a  bomb  calorimeter.  In  the  body,  proteids  yield  certain  de- 
composition products  which  are  removed  through  the  excreta, 
and  which  represent  a  certain  quantity  of  potential  energy 
thus  lost  to  the  economy.  The  average  fuel  value  of  pro- 
teids burned  outside  of  the  body  is  placed  at  5711  calories 


POODS  AND  THEIR,  DIGESTION  15 

per  gram,1  or  5.7  large  calories.  Deducting  the  heat  value 
of  the  proteid  decomposition  products  contained  in  the  ex- 
creta, the  physiological  fuel  value  of  proteids  is  reduced  on 
an  average  to  about  4.1  large  calories  per  gram.2  Rubner 
considers  that  the  physiological  fuel  value  of  vegetable  pro- 
teids is  somewhat  less  than  that  of  animal  proteids ;  con- 
glutin,  for  example,  yielding  3.96  calories,  as  contrasted 
with  4.3  calories  furnished  by  egg-albumin,  or  4.40  calories 
from  casein.  On  a  mixed  diet,  where  60  per  cent  of  the 
ingested  proteid  food  is  of  animal  origin  and  40  per  cent 
vegetable,  the  fuel  value  available  to  the  body  would  be 
about  4.1  calories  per  gram  of  proteid,  on  the  assumption 
that  the  physiological  heat  value  of  vegetable  proteids  aver- 
ages 3.96  calories  per  gram  and  that  of  animal  proteids  4.23 
calories  per  gram  (Rubner). 

At  present,  we  accept  for  all  purposes  of  computation  the 
following  figures  as  representing  the  physiological  or  avail- 
able (to  the  body)  fuel  value  of  the  three  classes  of  organic 
foodstuffs : 

1  gram  of  proteid 4.1  Large  Calories 

1  gram  of  fat 9.3       "  " 

1  gram  of  carbohydrate 4.1       "          «' 

From  these  data,  it  is  evident  at  a  glance  that  1  gram  of 
fat  is  isodynamic  with  2.27  grams  of  either  carbohydrate  or 
proteid ;  and  since  carbohydrate  and  fat  are  of  use  to  the 
body  mainly  because  of  their  energy  value,  it  is  obvious  that 
50  grams  of  fat  taken  as  food  will  be  of  as  much  service  to 
the  body  as  113  grams  of  starch.  In  view  of  the  relatively 
high  fuel  value  of  fats,  it  follows  that  the  physiological  heat 
of  combustion  of  any  given  food  material  will  correspond 


1  Stohmann:  Ueber  den  Warmewerth  der  Bestandtheile  der  Nahrtingsraittel. 
Zeitschr.  f.  Biol.,  Band  31,  p.  373. 

2  See  Rubner  :  Calorimetrische  Untersuchungen.    Zeitschr.  f.  Biol.,  Band  21, 
p.  250.  Also,  Rubner:  Die  Quelle  der  thierischen  Warme.  Ibid.,  Band  30,  p.  73. 


16  THE  NUTRITION   OF  MAN 

largely  with  the  content  of  fat  therein.  This  is  quite 
apparent  from  the  data  given  in  the  table  showing  chemical 
composition  of  food  materials,  where  the  fuel  value  per  pound 
is  seen  to  run  more  or  less  closely  parallel  with  the  per- 
centage of  fat.  Experience,  as  well  as  direct  physiological 
experiment,  teaches  us,  however,  that  fat  and  carbohydrate 
cannot  be  interchanged  indefinitely,  because  of  the  difficulty 
in  utilization  of  fat  when  the  amount  is  increased  beyond  a 
certain  point.  Personal  experience  provides  ample  evidence 
of  the  difference  in  availability  between  the  two  classes  of 
foodstuffs.  Carbohydrates  are  easily  utilizable,  fats  with 
more  difficulty.  Palate,  as  well  as  stomach,  rebels  at  large 
quantities  of  fat;  a  statement  that  certainly  holds  good  for 
most  civilized  people,  though  exceptions  may  be  found,  as  in 
the  Esquimeaux  and  certain  savage  races. 

In  the  nourishment  of  the  body,  the  various  factors  that  aid 
in  the  utilization  of  food  are  of  great  moment  and  must  not 
be  overlooked.  It  is  not  enough  that  the  body  be  supplied 
with  the  proper  proportion  of  nutrients,  with  sufficient  pro- 
teid  to  meet  the  demand  for  nitrogen,  and  with  carbohydrate 
and  fat  adequate  to  yield  the  needed  energy;  but  all  those 
physiological  processes  which  have  to  do  with  the  prepara- 
tion of  the  foodstiiffs  for  absorption  into  the  circulating  blood 
and  lymph  must  be  in  effective  working  order.  There  is  an 
intricacy  of  detail  here  which  calls  for  careful  oversight,  and 
it  is  one  of  the  functions  of  the  nervous  system  to  control 
and  regulate  both  the  mechanical  and  the  chemical  processes 
that  are  concerned  in  this  seemingly  automatic  progression 
of  foodstuffs  from  their  entry  into  the  mouth  cavity  to  their 
final  discharge  from  the  alimentary  tract,  after  removal  of 
the  last  vestige  of  true  nutritive  material. 

Mastication ;  deglutition ;  secretion  of  the  various  digestive 
juices,  saliva,  gastric  juice,  pancreatic  juice,  bile,  intestinal 
juice,  etc. ;  peristalsis,  or  the  rhythmical  movements  of  the 


FOODS  AND  THEIR  DIGESTION  17 

muscular  walls  of  the  gastro-intestinal  tract;  the  solvent 
action  of  the  several  digestive  fluids  on  the  different  types 
of  foodstuffs;  the  absorption  of  the  products  formed  as  a 
preliminary  step  in  their  transportation  to  the  tissues  and 
organs  of  the  body,  where  they  are  to  serve  their  ultimate  pur- 
pose in  nutrition;  the  interaction  of  these  several  processes 
one  on  the  other;  and,  finally,  the  influence  of  the  various 
nerve  fibres  and  nerve  centres  concerned  in  the  control  of 
these  varied  activities,  —  all  must  work  together  in  harmony 
and  precision  if  the  full  measure  of  available  nitrogen  and 
energy-yielding  material  is  to  be  extracted  and  absorbed 
from  the  ingested  food,  without  undue  expenditure  of  physio- 
logical labor.  Further,  the  various  processes  of  cell  and 
tissue  metabolism,  by  which  the  absorbed  food  material  is 
built  up  into  living  protoplasm,  and  the  chemical  processes 
of  oxidation,  hydrolysis,  reduction,  etc.,  by  which  the  intra 
and  extra  cellular  material  is  broken  down  progressively  into 
varied  katabolic  or  excretory  products,  with  liberation  of 
energy ;  all  these  must  move  forward  harmoniously  and  with 
due  regard  to  the  preservation  of  an  even  balance  between 
intake  and  outgo,  if  the  nutrition  of  the  body  is  to  be  main- 
tained at  a  proper  level,  and  with  that  degree  of  physiological 
economy  which  is  coincident  with  good  health  and  high 
efficiency. 

We  may  well  pause  here  and  consider  briefly  some  of  these 
processes  which  play  so  prominent  a  part  in  the  proper  utiliza- 
tion of  the  three  classes  of  organic  foodstuffs.  The  first 
digestive  fluid  which  the  ingested  food  comes  in  contact 
with  is  the  saliva.  Sensory  nerve  fibres,  chiefly  of  the 
glossopharyngeal  and  lingual  nerves  which  supply  the  mouth 
and  tongue,  are  stimulated  by  the  sapid  substances  of  the 
food,  and  likewise  by  mere  contact  of  the  food  particles  with 
the  mucous  membrane  lining  the  mouth  cavity  as  the  food  is 
masticated  and  rolled  about  prior  to  deglutition.  Impulses 

2 


18  THE  NUTRITION  OF  MAN 

communicated  in  this  way  to  the  above  sensory  nerves  are 
transmitted  to  certain  nerve  centres  in  the  medulla  oblongata, 
whence  impulses  are  reflected  back  through  secretory  nerves 
going  to  the  individual  salivary  glands,  thereby  calling  forth 
a  secretion.  The  production  of  saliva  is  thus  a  simple  reflex 
act,  in  which  the  food  consumed  serves  as  a  true  stimulant 
or  excitant.  Pawlow,1  indeed,  claims  a  certain  degree  of 
adaptability  of  the  secretion  to  the  character  of  the  food 
taken  into  the  mouth.  Thus,  he  finds  that  dry,  solid  food 
excites  a  large  flow  of  saliva,  such  as  would  be  needed  to 
masticate  it  properly  and  bring  it  into  a  suitable  condition 
for  swallowing.  On  the  other  hand,  foods  containing  an 
abundance  of  water  cause  only  a  scanty  flow  of  saliva.  The 
situation  of  this  secretory  centre  in  the  medulla,  and  the  many 
branchings  of  nerve  cells  in  this  locality  would  naturally 
suggest  the  possibility  of  salivary  secretion  being  incited  by 
stimuli  from  a  variety  of  sources.  This  is  indeed  the  case, 
and  it  is  worthy  of  note  that  a  flow  of  saliva  may  result  from 
stimulation  of  the  sensory  fibres  of  the  vagus  nerves  as  well 
as  of  the  splanchnic  and  sciatic,  thus  indicating  how  a  given 
secreting  gland  may  be  called  into  activity  by  impulses  or 
stimuli  which  come  to  the  centre  through  very  indirect  and 
devious  pathways.  Further,  the  secretory  centre  may  be 
stimulated,  and  likewise  inhibited,  by  impulses  which  have 
their  origin  in  higher  nerve  centres  in  the  brain,  These 
facts  are  of  great  importance  in  throwing  light  upon  the 
ways  in  which  a  secretion  like  saliva  is  called  forth  and  its 
digestive  action  thus  made  possible.  The  thought  and  the 
odor  of  savory  food  cause  the  mouth  to  water,  the  flow  of 
saliva  so  incited  being  the  result  of  psychical  stimulation. 
Similarly,  fear,  embarrassment,  and  anxiety  frequently  cause 
a  dry  mouth  and  parched  throat  through  inhibition  of  the 

1  Pawlow :  The  Work  of  the  Digestive  Glands.    Translated  by  Thompson. 
London,  1902. 


FOODS   AND   THEIR  DIGESTION  19 

secretory  centre  by  impulses  which  have  their  origin  in  higher 
centres  in  the  brain. 

The  application  of  these  facts  to  our  subject  is  perfectly 
obvious,  since  they  suggest  at  once  how  the  production  or 
secretion  of  an  important  digestive  fluid  —  upon  which  the 
utilization  of  a  given  class  of  foodstuffs  may  be  quite  de- 
pendent—  is  controlled  and  modified  through  the  nervous 
system  by  a  variety  of  circumstances.  We  might  reason 
that  the  appearance,  odor,  and  palatability  of  food  are  factors 
of  prime  importance  in  its  utilization  by  the  body;  that  the 
aesthetics  of  eating  are  not  to  be  ignored,  since  they  have  an 
important  influence  upon  the  flow  of  the  digestive  secretions. 
A  peaceful  mind,  pleasurable  anticipation,  freedom  from 
care  and  anxiety,  cheerful  companionship,  all  form  desirable 
table  accessories  which  play  the  part  of  true  psychical  stimuli 
in  accelerating  the  flow  of  the  digestive  juices  and  thus  pave 
the  way  for  easy  and  thorough  digestion.  Further,  it  is 
easy  to  see  how  thorough  mastication  of  food  may  prolong 
mechanical  stimulation  of  the  salivary  glands  and  thus  in- 
crease the  flow  of  the  secretion,  while  the  longer  stay  of 
sapid  substances  in  the  mouth  cavity  increases  the  duration 
of  the  chemical  stimulation  of  the  sensory  fibres  of  the  lingual 
and  glossopharyngeal  nerves.  In  this  connection,  we  may  cite 
the  view  recently  advanced  by  Pawlow  that  the  individual 
salivary  glands  respond  normally  to  different  stimuli.  Thus, 
there  are  three  pairs  of  salivary  glands  concerned  in  the  pro- 
duction of  saliva,  —  the  submaxillary,  parotid,  and  sublingual, 
—  all  of  which  pour  their  secretions  through  separate  ducts 
into  the  mouth  cavity.  By  experiment,  Pawlow  has  found 
that  in  the  dog  the  submaxillary  gland  yields  a  copious  flow 
of  saliva  when  stimulated  by  acids,  the  chewing  of  meats, 
the  sight  of  food,  etc.,  while  the  parotid  gland  fails  to  respond. 
On  the  other  hand,  the  latter  gland  responds  with  an  abun- 
dant secretion  when  dry  food,  such  as  dry  powdered  meat, 


20  THE  NUTRITION  OF  MAN 

dried  bread,  etc.,  is  placed  in  the  mouth.  With  this  gland, 
the  inference  is  that  dryness  is  the  active  stimulus. 

As  a  digestive  secretion,  saliva  serves  several  important 
purposes.  By  moistening  the  food  it  renders  mastication  and 
deglutition  possible;  its  natural  alkalinity  tends  to  neutral- 
ize somewhat  such  acidity  as  may  be  present  in  the  food  ; 
it  dissolves  various  solid  substances,  thus  making  a  solution 
capable  of  stimulating  the  taste  nerves;  lastly,  and  most 
important,  it  has  a  marked  digestive  and  solvent  action  on 
starchy  foods.  A  large  proportion  of  the  non -nitrogenous 
food  consumed  by  man  —  in  most  countries  —  is  composed  of 
some  form  of  starch,  and  this  the  body  cannot  use  until  it 
has  undergone  conversion  into  soluble  forms,  such  as  dex- 
trins  and  sugar.  This  it  is  the  function  of  saliva  to  accom- 
plish, and  it  owes  its  activity  in  this  direction  to  the  presence 
of  a  soluble  ferment  or  enzyme  known  as  ptyalin. 

Enzymes,  which  play  so  important  a  part  in  all  digestive 
processes,  are  a  peculiar  class  of  substances  produced  by  the 
living  cells  which  constitute  the  various  secreting  glands. 
They  are  of  unknown  composition,  and  are  peculiar  in  that 
the  chemical  changes  they  induce  are  the  result  of  what  is 
termed  catalysis,  i.  e.,  contact.  That  is,  the  enzyme  or  cata- 
lyzer does  not  enter  into  the  reaction,  it  is  not  destroyed 
or  used  up,  but  by  its  mere  presence  sets  in  motion  or 
accelerates  a  reaction  between  two  other  substances.  The 
ordinary  illustration  from  the  inorganic  world  is  spongy 
platinum,  which,  if  placed  in  contact  with  a  mixture  of 
oxygen  and  hydrogen,  causes  the  two  gases  to  unite  with 
formation  of  water,  although  the  two  gases  alone  at  ordi- 
nary temperature  will  not  so  combine.  In  this  reaction  the 
platinum  is  not  altered,  neither  does  it  apparently  enter  into 
the  reaction;  it  is  a  simple  catalyzer.  The  chemical  nature  of 
the  change  which  most  digestive  enzymes  produce  is  usually 
defined  as  hydrolytic,  in  which  the  substance  undergoing 


FOODS  AND  THEIK  DIGESTION  21 

transformation  is  made  to  combine  with  water,  thus  becoming 
hydrolyzed,  this  reaction  generally  being  accompanied  by  a 
cleavage  or  splitting  of  the  molecule  into  simpler  substances. 
It  is  to  be  noted  further  that  enzymes  are  specific  in  their 
action.  An  enzyme  that  acts  upon  starch,  for  example,  can- 
not act  on  proteids  or  fats.  Some  digestive  fluids  have  the 
power  of  producing  changes  in  different  classes  of  foodstuffs, 
but  such  diversity  of  action  is  always  assumed  to  be  due  to 
the  presence  in  the  same  fluid  of  different  enzymes.  Emil 
Fischer l  has  advanced  the  theory  that  the  specificity  of  an 
enzyme  is  related  to  the  geometrical  structure  of  the  sub- 
stance undergoing  change;  i.  e.,  that  .each  enzyme  is  capable 
of  acting  upon  or  attaching  itself  only  to  such  molecules 
as  have  a  definite  structure  with  which  the  enzyme  is  in  har- 
mony. Or,  the  enzyme  may  be  considered  as  a  key  which  will 
fit  only  into  the  lock  (structure)  of  the  molecule  it  acts  upon. 
One  characteristic  feature  of  enzymes  is  the  incomplete- 
ness of  their  action.  Thus,  the  enzyme  of  saliva  transforms 
starch  by  a  series  of  progressive  changes  into  soluble  starch, 
two  or  more  dextrins,  and  the  sugar  maltose  as  the  chief  end- 
product.  A  mixture  of  starch  paste  and  saliva  under  ordi- 
nary conditions,  however,  never  results  in  the  formation  of 
a  hundred  per  cent  of  maltose,  but  there  always  remains  a 
variable  amount  of  dextrin  which  appears  to  resist  further 
change.  This  is  apparently  due  to  what  is  known  as  the  re- 
versible action  of  enzymes.  Thus,  the  chemical  reactions 
involved  here  are  reversible  actions,  i.  e.,  they  take  place  in 
opposite  directions.  The  catalyzer  not  only  accelerates  or 
incites  a  reaction  in  the  direction  of  breaking  down  the  sub- 
stance acted  upon,  but  it  also  aids  in  the  recomposition  of 
the  products  so  formed  into  the  original  or  kindred  substance. 
With  reversible  reactions  of  this  sort  the  opposite  changes 

1  Emil  Fischer:  Bedeutung der  Stereochemie  fiir  die  Physiologic.   Ztttschr. 
fur  physiologische  Chemie,  Band  26,  p.  60. 


22  THE   NUTRITION  OF  MAN 

sooner  or  later  strike  an  equilibrium,  which  remains  con- 
stant until  some  alteration  in  the  conditions  brings  about  an 
inequality  and  the  reactions  proceed  until  a  new  equilibrium 
is  established.  In  the  body,  however,  where  the  circulating 
blood  and  lymph  provide  facilities  for  the  speedy  removal  by 
absorption  of  the  soluble  products  formed,  the  reaction  may 
proceed  until  the  original  substance  undergoing  change  is 
completely  transformed  into  the  characteristic  end-product. 
This  reversible  action  of  enyzmes  is  an  important  feature, 
and  helps  explain  certain  nutritional  changes  to  be  referred 
to  later.  Whether  all  enzymes  behave  in  this  way  is  not  as 
yet  determined. 

Another  peculiarity  of  digestive  enzymes  is  their  extreme 
sensitiveness  to  changes  in  their  environment.  Powerful  in 
their  ability  to  transform  relatively  large  quantities  of  a 
given  foodstuff  into  simple  products  better  adapted  for  absorp- 
tion and  utilization  by  the  body,  they  are,  however,  quickly 
checked  in  their  action,  and  even  destroyed,  when  the  condi- 
tions surrounding  them  are  slightly  interfered  with.  They 
require  for  their  best  action  a  temperature  closely  akin  to 
that  of  the  healthy  body,  and  any  great  deviation  therefrom 
will  result  at  once  in  an  inhibition  of  their  activity.  Further, 
they  demand  a  certain  definite  reaction  of  the  fluid  or  mix- 
ture, if  their  working  power  is  to  be  maintained  at  the  maxi- 
mum. Indeed,  many  enzymes,  like  the  ptyalin  of  saliva,  are 
quickly  destroyed  if  the  reaction  is  greatly  changed.  En- 
zymes are  thus  seen  to  be  more  or  less  unstable  substances, 
endowed  with  great  power  as  digestive  agents,  but  sensitive 
to  a  high  degree  and  working  advantageously  only  under 
definite  conditions.  Many  perversions  of  digestion  and  of 
nutrition  are  connected  not  only  with  a  lack  of  the  proper 
secretion  of  some  one  or  more  digestive  enzyme,  but  also 
with  the  lack  of  proper  surroundings  for  the  manifesta- 
tion of  normal  or  maximum  activity. 


FOODS   AND   THEIR  DIGESTION  23 

With  these  statements  before  us,  we  can  readily  picture  for 
ourselves  the  initial  results  following  the  ingestion  of  starch- 
containing  foods  properly  cooked ;  and  it  may  be  mentioned 
here  that  the  cooking  is  an  essential  preliminary,  for  uncooked 
starch  cannot  be  utilized  in  any  degree  by  man.  With  the 
mind  in  a  state  of  pleasurable  anticipation,  with  freedom 
from  care  and  worry,  which  are  so  liable  to  act  as  deterrents 
to  free  secretion,  and  with  the  food  in  a  form  which  appeals 
to  the  eye  as  well  as  to  the  olfactories,  its  thorough  mastica- 
tion calls  forth  and  prolongs  vigorous  salivary  secretion,  with 
which  the  food  becomes  intimately  intermingled.  Salivary 
digestion  is  thus  at  once  incited,  and  the  starch  very  quickly 
commences  to  undergo  the  characteristic  change  into  soluble 
products.  As  mouthful  follows  mouthful,  deglutition  alter- 
nates with  mastication,  and  the  mixture  passes  into  the 
stomach,  where  salivary  digestion  can  continue  for  a  limited 
time  only,  until  the  secretion  of  gastric  juice  eventually  es- 
tablishes in  the  stomach-contents  a  distinct  acid  reaction, 
when  salivary  digestion  ceases  through  destruction  of  the 
starch-converting  enzyme.  Need  we  comment,  in  view  of 
the  natural  brevity  of  this  process,  upon  the  desirability  for 
purely  physiological  reasons  of  prolonging  within  reasonable 
limits  the  interval  of  time  the  food  and  saliva  are  com- 
mingled in  the  mouth  cavity?  It  seems  obvious,  in  view  of 
the  relatively  large  bulk  of  starch-containing  foods  consumed 
daily,  that  habits  of  thorough  mastication  should  be  fostered, 
with  the  purpose  of  increasing  greatly  the  digestion  of  starch 
at  the  very  gateway  of  the  alimentary  tract.  It  is  true  that 
in  the  small  intestine  there  comes  later  another  opportunity 
for  the  digestion  of  starch;  but  it  is  unphysiological,  as  it  is 
undesirable,  for  various  reasons,  not  to  take  full  advantage  of 
the  first  opportunity  which  Nature  gives  for  the  preparation 
of  this  important  foodstuff  for  future  utilization.  Further, 
thorough  mastication,  by  a  fine  comminution  of  the  food 


24  THE  NUTRITION  OF  MAN 

particles,  is  a  material  aid  in  the  digestion  which  is  to  take 
place  in  the  stomach  and  intestine.  Under  normal  conditions, 
therefore,  and  with  proper  observance  of  physiological  good 
sense,  a  large  proportion  of  the  ingested  starchy  foods  can  be 
made  ready  for  speedy  absorption  and  consequent  utilization 
through  the  agency  of  salivary  digestion. 

Nowhere  in  the  body  do  we  find  a  more  forcible  illustra- 
tion of  economical  method  in  physiological  processes  than  in 
the  mechanism  of  gastric  secretion.  Years  ago,  it  was  thought 
that  the  flow  of  gastric  juice  was  due  mainly  to  mechanical 
stimulation  of  the  gastric  glands  by  contact  of  the  food 
material  with  the  lining  membrane  of  the  stomach.  This, 
however,  is  not  the  case,  as  Pawlow  has  clearly  shown,  and 
it  is  now  understood  that  the  flow  of  gastric  juice  is  started  by 
impulses  which  have  their  origin  in  the  mouth  and  nostrils  ; 
the  sensations  of  eating,  the  smell,  sight,  and  taste  of  food 
serving  as  psychical  stimuli,  which  call  forth  a  secretion  from 
the  stomach  glands,  just  as  the  same  stimuli  may  induce  an 
outpouring  of  saliva.  These  sensations,  as  Pawlow  has  ascer- 
tained, affect  secretory  centres  in  the  brain,  and  impulses  are 
thus  started  which  travel  downward  to  the  stomach  through 
the  vagus  nerves,  and  as  a  result  gastric  juice  begins  to  flow. 
This  process,  however,  is  supplemented  by  other  forms  of 
secretion,  likewise  reflex,  which  are  incited  by  substances, 
ready  formed  in  the  food,  and  by  substances  —  products  of 
digestion  —  which  are  manufactured  from  the  food  in  the 
stomach.  Soups,  meat  juice,  and  the  extractives  of  meat, 
likewise  dextrin  and  kindred  products,  when  present  in  the 
stomach,  are  especially  active  in  provoking  secretion.  Sub- 
stances which  in  themselves  have  less  flavor,  as  water,  milks 
etc.,  are  far  less  effective  in  this  direction,  while  the  white 
of  eggs  and  bread  are  entirely  without  action  in  directly 
stimulating  secretion.  When  the  latter  foods  have  been  in 
the  stomach  for  a  time,  however,  and  the  proteid  material  has 


FOODS  AND  THEIK  DIGESTION  25 

undergone  partial  digestion,  then  absorption  of  the  products 
so  formed  calls  forth  energetic  secretion  of  gastric  juice.  It 
is  thus  seen  that  there  are  three  distinct  ways  —  all  reflex  — 
by  which  gastric  juice  is  caused  to  flow  into  the  stomach  as 
a  prelude  to  gastric  digestion.  Further,  it  has  been  shown 
by  Pawlow  that  there  is  a  relationship  between  the  volume 
and  character  of  the  gastric  juice  secreted  and  the  amount 
and  composition  of  the  food  ingested,  thus  suggesting  a  cer- 
tain adjustment  in  the  direction  of  physiological  economy 
well  worthy  of  note.  A  diet  of  bread,  for  example,  leads  to 
the  secretion  of  a  smaller  volume  of  gastric  juice  than  a  cor- 
responding weight  of  meat  produces,  but  the  juice  secreted 
under  the  influence  of  bread  is  richer  in  pepsin  and  acid,  i.  e., 
it  has  a  greater  digestive  action  than  the  juice  produced  by 
meat.  The  suggestion  is  that  gastric  juice  assumes  different 
degrees  of  concentration,  with  different  proportions  of  acid 
and  pepsin,  to  meet  the  varying  requirements  of  a  changing 
dietary. 

As  has  been  indicated,  pepsin  and  hydrochloric  acid  are 
the  important  constituents  of  gastric  juice.  It  is  noteworthy, 
however,  that  it  is  the  combination  of  the  two  that  is  effect- 
ive in  digestion.  Pepsin  without  acid  is  of  no  avail,  and 
acid  without  pepsin  can  accomplish  little  in  the  digestion  of 
food.  Pepsin  and  acid  are  secreted  by  different  gland  cells 
in  the  stomach,  and  gastric  insufficiency,  or  so-called  in- 
digestion, may  arise  from  either  a  condition  of  apepsia  or 
from  hypoacidity.  It  is  worthy  of  comment  that  the  amount 
of  hydrochloric  acid  secreted  during  24  hours  by  the  normal 
individual,  under  ordinary  .conditions  of  diet,  amounts  to 
what  would  constitute  a  fatal  dose  of  acid  if  taken  at  one  time 
in  concentrated  form.  At  the  outset  of  gastric  secretion,  the 
fluid  shows  only  a  slight  degree  of  acidity,  but  as  secretion 
proceeds,  the  acidity  rises  to  0.2-0.3  per  cent  of  hydrochloric 
acid.  The  main  action  of  gastric  juice  is  exerted  on  proteid 


26  THE  NUTEITIOK  OF  MAN 

foods,  which  under  its  influence  are  gradually  dissolved  and 
converted  into  soluble  products  known  as  proteoses  and  pep- 
tones. It  is  a  process  of  peptonization,  in  which  the  proteid 
of  the  food  is  gradually  broken  down  into  so-called  hydrolytic 
cleavage  products.  The  enzyme,  like  the  ptyalin  of  saliva, 
is  influenced  by  temperature,  maximum  digestive  action  being 
manifested  at  about  38°  C.,  the  temperature  of  the  body. 
Further,  a  certain  degree  of  acidity  is  essential  for  procuring 
the  highest  degree  of  efficiency.  Ordinarily,  it  is  stated  that 
digestive  action  proceeds  best  in  the  presence  of  0.2  per  cent 
hydrochloric  acid,  but  what  is  more  essential  for  vigorous 
digestion  is  a  certain  relationship  between  the  acid,  pepsin, 
and  proteid  undergoing  digestion.  As  pepsin  and  the  amount 
of  proteid  are  increased,  the  amount  of  acid,  and  its  percent- 
age somewhat,  must  be  correspondingly  increased  if  digestion 
is  to  be  maintained  at  the  maximum. 

Another  important  function  of  gastric  juice  is  that  of  cur- 
dling milk,  due  to  the  presence  in  the  secretion  of  a  peculiar 
enzyme  known  as  rennin.  The  latter  ferment  acts  upon  the 
casein  of  milk,  —  the  chief  proteid  constituent,  —  transform- 
ing it  into  a  related  substance  commonly  called  paracasein. 
This  then  reacts  with  the  calcium  salts  present  in  milk,  form- 
ing an  insoluble  curd  or  calcium  compound.  From  this  point 
on,  the  digestion  of  milk-casein  by  gastric  juice  is  the  same  as 
that  of  any  other  solid  proteid,  it  being  gradually  transformed 
by  the  pepsin-acid  into  soluble  cleavage  products.  Why  gas- 
tric juice  should  be  provided  with  this  special  enzyme,  capable 
of  acting  solely  on  the  casein  of  milk,  can  only  be  conjec- 
tured, but  we  may  assume  that  it  has  to  do  with  the  eco- 
nomical use  of  this  important  food.  As  the  sole  nutriment  of 
the  young,  milk  occupies  a  peculiar  position  as  a  foodstuff, 
and  being  a  liquid,  its  proteid  constituent  might  easily  escape 
complete  digestion  were  it  to  pass  on  too  hastily  through  the 
gastro-intestinal  tract.  Experiment  has  shown  that  when 


FOODS  AND  THEIR  DIGESTION  27 

liquid  food  alone  is  taken  into  the  stomach  it  is  pushed  for- 
ward into  the  small  intestine  in  a  comparatively  short  time. 
Curdled  as  it  is  by  rennin,  however,  casein  must  stay  for  a 
longer  period  in  the  stomach,  like  any  other  solid  food,  and 
its  partial  digestion  by  gastric  juice  thereby  made  certain. 
For  the  reasons  above  stated,  it  is  apparent  why  milk  should 
not  be  treated  as  a  drink  in  our  daily  diet.  Remembering 
that  when  milk  reaches  the  stomach  it  is  converted  into  a 
solid  clot  or  curd,  there  is  obvious  reason  for  sipping  it,  in- 
stead of  taking  it  by  the  glassful,  thereby  favoring  the  forma- 
tion of  small,  individual  clots  instead  of  one  large  curd,  and 
thus  facilitating  instead  of  retarding  digestion. 

Among  other  factors  in  gastric  digestion,  the  muscular 
movements  of  the  stomach  walls  are  to  be  emphasized,  since 
we  have  here  a  mechanical  aid  to  digestion  of  no  small  mo- 
ment, and  likewise  a  means  of  accomplishing  the  onward 
movement  of  the  stomach  contents.  The  outer  walls  of  the 
stomach  are  composed  of  a  thick  layer  of  circular  muscular 
fibres,  especially  conspicuous  at  the  pyloric  end  of  the  organ, 
where  the  latter  is  joined  on  to  the  intestine ;  a  smaller,  less 
conspicuous  layer  of  longitudinal  muscle  fibres,  and  some 
oblique  fibres.  At  the  pylorus,  the  circular  fibres  are  so 
arranged  as  to  form  a  structure  which,  aided  by  a  peculiar 
folding  of  the  inner  mucous  membrane,  serves  as  a  sphincter, 
closing  off  the  stomach  from  the  duodenum,  the  beginning  of 
the  small  intestine.  The  movements  of  the  stomach  were 
first  made  the  subject  of  careful  investigation  by  Dr.  Beau- 
mont in  his  study  of  the  celebrated  case  of  Alexis  St.  Martin, 
a  French  Canadian,  who,  in  1822,  was  accidentally  wounded 
by  the  discharge  of  a  musket,  with  the  resultant  formation  of 
a  permanent  fistulous  opening  in  the  stomach.  Dr.  Beau- 
mont, in  the  description l  of  his  observations,  writes  that  "  by 

1  The  Physiology  of  Digestion.  By  William  Beaumont,  M.D.  Second 
Edition,  1847,  p.  100- 


28  THE  NUTKITION   OF  MAN 

the  alternate  contractions  and  relaxations  of  these  bands  (of 
muscle)  a  great  variety  of  motion  is  induced  on  this  organ 
(the  stomach),  sometimes  transversely,  and  at  other  times 
longitudinally.  These  alternate  contractions  and  relaxations, 
when  affecting  the  transverse  diameter,  produce  what  are 
called  vermicular  or  peristaltic  motions.  .  .  .  When  they  all 
act  together,  the  effect  is  to  lessen  the  cavity  of  the  stomach, 
and  to  press  upon  the  contained  aliment,  if  there  be  any  in 
the  stomach.  These  motions  not  only  produce  a  constant 
disturbance,  or  churning  of  the  aontents  of  this  organ,  but 
they  compel  them,  at  the  same  time,  to  revolve  around  the 
interior,  from  point  to  point,  and  from  one  extremity  to  the 
other."  Of  more  recent  investigations,  the  most  important 
are  those  made  by  Cannon,1  with  the  X-ray  apparatus.  From 
these  later  studies,  it  is  evident  that  Dr.  Beaumont's  view  of 
the  entire  stomach  being  involved  in  a  general  rotary  move- 
ment is  not  correct,  since  in  reality  the  movements  are  con- 
fined mainly  to  the  pylori  c  end  of  the  stomach,  the  fund  us 
or  portion  nearer  the  oesophagus  not  being  directly  involved. 
This  means  that  when  food  material  passes  into  the  stomach, 
it  may  remain  at  the  fundic  end  for  some  time  more  or  less 
undisturbed  before  admixture  with  the  gastric  juice  occurs, 
and  under  such  conditions,  until  acidity  creeps  in,  the  salivary 
digestion  of  starch  can  continue. 

According  to  the  observations  of  Cannon,  the  contractile 
movements  of  the  stomach  commence  shortly  after  the  en- 
trance of  food,  the  contractions  starting  from  about  the 
middle  of  the  stomach  and  passing  on  toward  the  pylorus. 
These  waves  of  contraction  follow  each  other  very  closely, 
certainly  not  more  than  one  or  two  minutes  apart,  and  per- 
haps less,  while  the  resulting  movements  bring  about  an 
intimate  commingling  of  food  and  gastric  juice  in  the  pyloric 

1  W.  B.  Cannon  :  The  Movements  of  the  Stomach  studied  by  means  of  the 
Bontgen  Rays.  American  Journal  of  Physiology,  vol.  1,  p.  359. 


FOODS  AND   THEIR  DIGESTION  29 

portion  of  the  stomach;  followed  by  a  gradual  diffusion  of 
the  semi-fluid  mixture  into  the  fundus  accompanied  by  a 
gradual  displacement  of  the  more  solid  food  in  the  latter 
region.  These  movements  of  the  stomach  are  more  or  less 
automatic,  arising  from  stimuli  —  the  acid  secreted  —  originat- 
ing in  the  stomach  itself,  although  it  is  considered  that  the 
movements  are  subject  to  some  regulation  from  extrinsic 
nerve  fibres,  such  as  the  vagi  and  the  splanchnics.  As  diges- 
tion proceeds  and  the  mass  in  the  stomach  becomes  more 
fluid,  the  pyloric  sphincter  relaxes  and  a  certain  amount  of 
the  fluid  material  is  forced  into  the  intestine  by  the  pressure 
of  the  contraction  wave.  This  is  repeated  at  varying  inter- 
vals, depending  presumably  in  some  measure  upon  the  con- 
sistency of  the  mass  in  the  stomach,  until  after  some  hours 
of  digestion  the  stomach  is  completely  emptied. 

Especially  interesting  and  suggestive  are  the  experiments 
made  by  Cannon  l  on  the  length  of  time  the  different  types 
of  foodstuffs  remain  in  the  stomach.  Using  cats  as  subjects, 
he  found  that  fats  remain  for  a  long  period  in  the  stomach ; 
they  leave  that  organ  slowly,  the  discharge  into  the  intes- 
tine being  at  about  the  same  rate  as  the  absorption  of  fat 
from  the  small  intestine  or  its  passage  into  the  large  intestine. 
Carbohydrate  foods,  on  the  other  hand,  begin  to  leave  the 
stomach  soon  after  their  ingestion.  They  pass  out  rapidly, 
and  at  the  end  of  two  hours  reach  a  maximum  amount  in  the 
small  intestine  almost  twice  the  maximum  for  proteids,  and 
two  and  a  half  times  the  maximum  for  fats,  both  of  which 
maxima  are  reached  only  at  the  end  of  four  hours.  Carbohy- 
drates remain  in  the  stomach  about  half  as  long  as  proteids. 
Proteids,  Cannon  finds,  frequently  do  not  leave  the  stomach 
at  all  during  the  first  half-hour  after  they  are  eaten.  After 


1  W.  B.  Cannon :  The  Passage  of  different  Food-stuffs  from  the  Stomach 
and  through  the  ^Small  Intestine.  American  Journal  of  Physiology,  vol.  12, 
p.  387. 


30  THE  NUTRITION   OF  MAN 

two  hours,  they  accumulate  in  the  small  intestine  to  a  degree 
only  slightly  greater  than  that  reached  by  carbohydrates  an 
hour  and  a  half  earlier.  The  departure  of  proteids  from  the 
stomach  is  therefore  slower  at  first  than  that  of  either  fats  or 
carbohydrates.  When  a  mixture  of  equal  parts  of  carbohy- 
drates and  proteids  is  fed,  the  discharge  from  the  stomach  is 
intermediate  in  rapidity.  When  fat  is  added  to  either  carbo- 
hydrates or  proteids  it  retards  the  passage  of  both  foodstuffs 
through  the  pylorus. 

It  is  evident  from  what  has  been  stated  that  the  gastric 
digestion  of  proteid  foods  is  a  comparatively  slow  process, 
involving  several  hours  of  time ;  and  further,  that  food  mate- 
rial in  general  remains  in  the  stomach  for  varying  periods, 
dependent  upon  its  chemical  composition.  It  would  appear 
further,  that  relaxation  of  the  pyloric  sphincter,  allowing 
passage  of  chyme  into  the  intestine,  must  depend  somewhat 
upon  chemical  stimulation,  as  this  offers  the  most  plausible 
explanation  of  the  diversity  of  action  seen  with  the  different 
foodstuffs.  As  has  been  pointed  out,  gastric  digestion  is 
primarily  a  process  for  the  conversion  of  proteid  food  into 
soluble  products.  It  would  be  a  mistake,  however,  to  assume 
that  the  digestion  of  proteid  foods  is  complete  in  the  stomach. 
Stomach  digestion  is  to  be  considered  more  as  a  preliminary 
step,  paving  the  way  for  further  changes  to  be  carried  for- 
ward by  the  combined  action  of  intestinal  and  pancreatic 
juice  in  the  small  intestine.  The  importance  of  gastric  diges- 
tion is  frequently  overrated.  It  is  unquestionably  an  impor- 
tant process,  but  not  absolutely  essential  for  the  maintenance 
of  life.  Dogs  have  lived  and  flourished  with  their  stomachs 
removed,  the  intestine  being  joined  to  the  oesophagus.  The 
intestine  is  a  much  more  important  part  of  the  alimentary 
tract;  it  is  likewise  far  more  sensitive  to  changing  conditions 
than  the  stomach,  and  undoubtedly  one  function  of  the  latter 
organ  is  to  protect  the  intestine  and  preserve  it  from  insult. 


FOODS  AND  THEIE  DIGESTION  31 

The  stomach  may  be  compared  to  a  vestibule  or  reservoir, 
capable  of  receiving  without  detriment  moderately  large 
amounts  of  food,  together  with  fluid,  in  different  forms  and 
combinations,  with  the  power  to  hold  them  there  until  by 
action  of  the  gastric  juice  they  are  so  transformed  that  their 
onward  passage  into  the  intestine  can  be  permitted  with  per- 
fect safety.  Then,  small  portions  of  the  properly  prepared 
material  may  be  discharged  from  time  to  time  through  the 
pylorus  without  danger  of  overloading  the  intestine,  and  iu 
a  form  capable  of  undergoing  rapid  and  complete  digestion, 
Further,  the  stomach  as  a  reservoir  is  very  useful  in  bring- 
ing  everything  to  a  proper  and  constant  temperature  before 
allowing  its  entry  into  the  intestine.  Another  fact  of  somo 
importance  is  that,  contrary  to  the  general  view,  absorption 
from  the  stomach  of  the  products  of  digestion  is  not  very 
rapid  under  ordinary  conditions.  Even  water  and  soluble 
salts  pass  very  slowly  into  the  circulation  from  the  stomach. 
Like  the  partially  digested  food  material,  they  are  carried 
forward  through  the  pyloric  sphincter  into  the  intestine, 
where  absorption  of  all  classes  of  material  is  most  marked. 
It  is  in  the  small  intestine  that  both  digestion  and  absorp- 
tion are  seen  at  their  best.  It  is  here  that  all  three  classes  of 
foodstuffs  are  acted  upon  simultaneously  through  the  agency 
of  the  pancreatic  juice,  intestinal  juice,  and  bile.  Here,  too, 
are  witnessed  some  of  the  most  complicated  and  interesting 
reactions  and  changes  occurring  in  the  whole  range  of  diges- 
tive functions.  Especially  noteworthy  is  the  peculiar  mech- 
anism by  which  the  secretion  of  pancreatic  juice  is  set  up  and 
maintained.  On  demand,  pancreatic  juice  is  manufactured 
in  the  pancreas  and  poured  into  the  intestine  just  beyond  the 
pylorus  through  a  small  duct  —  the  duct  of  Wirsung.  Secre- 
tion is  started  by  contact  of  the  acid  contents  of  the  stomach 
with  the  mucous  membrane  of  the  small  intestine,  so  that  as 
soon  as  the  acid  chyme  passes  through  the  pyloric  sphinctei 


32  THE  NUTRITION   OF  MAN 

there  commences  an  outflow  of  pancreatic  juice  into  the  in- 
testine. While  acid  is  plainly  the  inciting  agent  in  this 
secretory  process,  its  action  is  indirect.  It  does  not  cause 
secretion  through  reflex  action  on  nerve  fibres,  but  it  acts 
upon  a  substance  formed  in  the  mucous  membrane  of  the  in- 
testine, transforming  it  into  secretin,  which  is  absorbed  by 
the  blood  and  carried  to  the  pancreas,  where  it  excites  se- 
cretory activity.  As  would  be  expected  from  the  foregoing 
statements,  the  secretion  of  pancreatic  juice  commences  very 
soon  after  food  finds  its  way  into  the  stomach,  and  naturally 
increases  in  amount  with  the  onward  passage  of  acid  chyme 
into  the  intestine,  the  maximum  flow  being  obtained  in  the 
neighborhood  of  the  third  or  fourth  hour,  after  which  the 
secretion  gradually  decreases.  In  man,  it  is  estimated  on 
the  basis  of  one  or  two  observations  that  the  amount  secreted 
during  24  hours  is  about  700  cc.,  or  a  pint  and  a  half.  Care- 
ful experiments,  however,  tend  to  show  that  the  quantity  of 
secretion  depends  in  some  measure  at  least  upon  the  charac- 
ter of  the  food,  and  also  that  the  composition  of  the  secretion 
varies  with  the  character  of  the  food.  Thus,  on  a  diet  com- 
posed mainly  of  meat,  the  proteid-digesting  enzyme  is  es- 
pecially conspicuous,  while  on  a  bread  diet,  with  its  large 
content  of  starch,  the  starch-digesting  enzyme  is  increased  in 
amount.  In  other  words,  there  is  suggested  the  possibility 
of  an  adaptation  in  the  composition  of  the  secretion  to  the 
character  of  the  food  to  be  digested. 

Pancreatic  juice  is  an  alkaline  fluid,  rather  strongly  alka- 
line in  fact,  from  its  content  of  sodium  carbonate,  and  is 
especially  characterized  by  the  presence  of  at  least  three 
distinct  enzymes;  viz.,  trypsin,  a  proteid-digesting  ferment; 
lipase,  a  fat-splitting  enzyme;  and  amylopsin.  a  starch- 
digesting  enzyme.  It  has  already  been  pointed  out  how 
dependent  the  secretion  of  pancreatic  juice  is  upon  the  co- 
operation of  the  intestinal  mucous  membrane.  A  similar 


FOODS   AND  THEIR  DIGESTION  33 

dependence  is  found  when  the  digestive  activity  of  the  secre- 
tion is  studied.  As  just  stated,  pancreatic  juice  contains  a 
pro teid -digesting  enzyme.  This  statement,  however,  is  not 
strictly  correct,  for  if  the  secretion  is  collected  through  a 
cannula  so  that  it  does  not  come  in  contact  with  the  mucous 
membrane  of  the  intestine,  it  is  found  free  from  any  digest- 
ive action  on  proteids.  The  secretion  is  activated,  how- 
ever, by  contact  with  the  duodenal  membrane.  Expressed 
in  different  language,  pancreatic  juice  as  it  is  secreted  by  the 
gland  does  not  contain  ready -formed  trypsin;  it  does  con- 
tain, however,  an  inactive  pro-enzyme,  which,  under  the  in- 
fluence of  a  specific  substance  contained  in  the  intestinal 
mucous  membrane,  known  as  enterokinase,  is  transformed 
into  the  active  enzyme  trypsin.  There  is  thus  seen  another 
suggestive  example  of  the  close  physiological  relationship 
between  the  small  intestine  and  the  activity  of  the  pancreatic 
gland,  or  its  secretion. 

The  chemical  changes  taking  place  in  the  small  intestine 
are  many  and  varied.  The  acid  chyme,  with  its  admixture 
of  semi-digested  food  material,  as  it  passes  through  the  pyloric 
sphincter  into  the  small  intestine,  is  at  once  brought  into 
immediate  contact  with  bile,  pancreatic  juice,  and  intestinal 
juice,  all  of  which  are  more  or  less  alkaline  in  reaction.  As 
a  result,  the  acidity  of  the  gastric  juice  is  rapidly  overcome, 
and  the  enzyme  pepsin,  which  up  to  this  point  could  exert 
its  characteristic  digestive  action,  is  quickly  destroyed  by  the 
accumulating  alkaline  salts.  Pepsin  digestion  thus  gives  way 
to  trypsin  digestion,  —  most  effective  in  an  alkaline  medium, 
—  and  the  proteids  of  the  food,  already  semi -digested  by 
pepsin-acid,  are  further  transformed  by  trypsin;  aided  and 
abetted  by  another  enzyme,  known  as  erepsin,  secreted  by 
the  mucous  membrane  of  the  intestine.  These  two  enzymes 
are  much  more  powerful  agents  than  pepsin.  It  is  true  tha* 
they  begin  work  where  pepsin  left  off,  but  most  striking  is 

3 


34  THE  NUTRITION  OF  MAN 

the  character  of  the  end-products  which  result  from  their 
combined  action,  since  they  are  small  molecules  and  there 
is  a  surprising  diversity  of  them.  In  other  words,  while 
gastric  digestion  breaks  down  the  proteid  foodstuffs  into  solu- 
ble bodies,  such  as  proteoses  and  peptones  closely  related  to 
the  original  proteids,  in  pancreatic  digestion  as  it  takes  place 
in  the  intestine  there  is  a  profound  breaking  down,  or  dis- 
ruption of  the  proteid  molecule  into  a  row  of  comparatively 
simple  nitrogenous  fragments,  many  of  them  crystalline  bodies ; 
such  as  leucin,  tyrosin,  glutaminic  acid,  aspartic  acid,  arginin, 
lysin,  histidin,  etc.,  known  chemically  as  monoamino-acids 
and  diamino-acids.  We  have  no  means  of  knowing  to  how 
great  an  extent  these  more  profound  disruptive  changes  of 
the  proteid  molecule  take  place  in  the  intestine.  Whether 
practically  all  of  the  ingested  proteid  food  is  broken  down 
into  these  relatively  simple  compounds  prior  to  absorption,  or 
whether  only  a  small  fraction  suffers  this  change,  cannot  be 
definitely  stated. 

A  few  years  ago,  the  majority  of  physiologists  held  to  the 
view  that  in  the  digestion  of  proteid  food  all  that  was  essen- 
tial was  its  conversion  into  soluble  and  diffusible  forms  which 
would  permit  of  ready  absorption  into  the  blood.  The  belief 
was  prevalent  that,  since  the  proteid  of  the  food  was  destined 
to  make  good  the  proteid  of  the  blood  and  through  the  latter 
the  proteids  of  the  tissues,  any  change  beyond  what  was 
really  necessary  for  absorption  of  the  proteid  would  be  un- 
economical and  indeed  wasteful.  On  the  other  hand,  due 
weight  must  be  given  to  the  fact  that  in  trypsin  digestion, 
proteid  can  be  quickly  broken  down  into  simple  nitrogenous 
compounds,  and  that  in  the  enzyme  erepsin,  present  in  the 
mucous  membrane  of  the  intestine,  we  have  an  additional 
ferment  very  efficient  in  bringing  about  cleavage  of  proteoses 
and  peptone  into  amino-acids.  From  these  latter  facts  it  might 
be  argued  that,  in  the  digestion  of  proteid  foodstuffs  by  the 


FOODS  AND  THEIR  DIGESTION  35 

combined  action  of  gastric  and  pancreatic  juice  in  the  alimen- 
tary tract,  a  large  proportion  of  the  proteid  is  destined  to 
undergo  complete  conversion  into  amino-acids,  and  that  from 
these  fragments  the  body,  by  a  process  of  synthesis,  can  con- 
struct its  own  peculiar  type  of  proteid. 

This  latter  suggestion  is  worthy  of  a  moment's  further  con- 
sideration. As  is  well  known,  every  species  of  animal  has 
its  own  particular  typa  of  proteid,  adapted  to  its  particular 
needs.  The  proteids  of  one  species  directly  injected  into  the 
blood  of  another  species  are  incapable  of  serving  as  nutriment 
to  the  body,  and  frequently  act  as  poisons.  Man  in  his  wide 
choice  of  food  consumes  a  great  variety  of  proteids,  all  differ- 
ent in  some  degree  from  the  proteids  of  his  own  tissues.  Is 
it  not  possible,  therefore,  that  it  is  the  true  function  of  pan- 
creatic and  intestinal  digestion  to  break  down  the  different 
proteids  of  the  food  completely  into  simple  fragments,  so  that 
the  body  can  reconstruct  after  its  own  particular  pattern  the 
proteids  essential  for  its  nourishment?  Or,  we  can  follow 
the  suggestion  contained  in  the  work  of  Abderhalden,1  who 
finds  that  in  the  long  continued  digestion  of  various  proteids 
by  pancreatic  juice  there  results  in  addition  to  the  amino- 
acids  a  very  resistant  residue,  non-proteid  in  nature,  which 
is  termed  poly  pep  tid.  In  other  words,  Abderhalden  believes 
that  pepsin,  trypsin,  and  erepsin  are  not  capable  of  bringing 
about  a  complete  breaking  down  of  proteids  into  amino-acids, 
but  that  there  always  remains  a  nucleus  of  the  proteid  not 
strictly  proteid  in  nature,  though  related  thereto,  —  poly- 
peptid,  —  which  may  serve  as  a  starting-point  for  the  syn- 
thesis or  construction  of  new  proteid  molecules,  the  various 
amino-acids  being  employed  to  finish  out  the  structure  and 
give  the  particular  character  desired.  This  view,  however, 
is  rendered  somewhat  untenable  by  the  more  recent  experi- 


i  Emil  Abderhalden :  Abbau  und  Aufbau  der  Eiweisskorper  im  thierischen 
Organismus.    Zeitschr.  f.  physiologische  Chemie,  Band  44,  p.  27. 


36  THE  NUTRITION   OF  MAN 

ments  of  Cohnheim,1  who  claims  that  proteids  can  be  completely 
broken  down  by  pepsin,  trypsin,  and  erepsin,  and  consequently 
polypeptids  would  hardly  be  available  for  the  synthesis  of  pro- 
teids. Moreover,  Bergell  and  Lewin  2  have  ascertained  that 
there  is  present  in  the  liver  an  enzyme  or  ferment  which  has 
the  power  of  digesting  or  breaking  down  certain  dipeptids 
and  polypeptids  into  amino-acids.  Hence,  it  follows  that  if 
any  polypeptids  are  absorbed  from  the  intestine,  they  would 
naturally  be  carried  to  the  liver,  where  further  cleavage  into 
fragments  suitable  for  synthetical  processes  might  occur.  In 
any  event,  there  is  good  ground  for  the  belief  that  the  more 
or  less  complete  disruption  of  the  proteid  molecule  into  small 
fragments  renders  possible  a  synthetical  construction  of  new 
proteid  to  meet  the  demands  of  the  organism ;  a  fact  of  great 
importance  in  our  conception  of  the  possibilities  connected 
with  this  phase  of  proteid  nutrition. 

Fatty  foods  undergo  little  or  no  chemical  alteration  until 
they  reach  the  small  intestine.  During  their  stay  in  the 
stomach  they  naturally  become  liquid  from  the  heat  of 
the  body,  and  there  is  more  or  less  liberation  of  fat  from 
the  digestive  action  of  gastric  juice  on  cell  walls,  connective 
tissues,  etc.  Most  food  fat  is  in  the  form  of  so-called  neu- 
tral fat,  which  must  undergo  hydrolysis  or  saponification 
before  it  can  be  absorbed  and  thus  made  available  for  the 
body.  This  is  accomplished  by  the  enzyme  lipase,  or  steap- 
sin,  of  the  pancreatic  juice,  aided  indirectly  by  the  presence 
of  bile.  Under  the  influence  of  this  fat-splitting  enzyme  all 
neutral  fats,  whether  animal  or  vegetable,  are  broken  apart, 
through  hydrolysis,  into  glycerin  and  a  free  fatty  acid ;  the 
latter  reacting  in  some  measure  with  the  sodium  carbonate  of 


1  Otto  Cohnheim  :  Zur  Spaltung  des  Nahrungseiweisses   im  Darm.    Zeit- 
schrift  f.  physiologische  Chemie,  Band  49,  p.  64. 

2  Bergell  and  Lewin  :  Zeitschrift  fur  experitnentelle  Pathologic  und  Therapie, 
Band  3,  p.  425. 


FOODS  AND  THEIR  DIGESTION  37 

the  pancreatic  juice  to  form  a  sodium  salt,  or  soluble  soap, 
while  perhaps  the  larger  part  of  the  fatty  acid  is  held  in  solu- 
tion by  the  bile  present.  Soap,  free  acid,  and  glycerin  are  then 
absorbed  from  the  intestine  and  are  found  again  combined  in 
the  lymph  as  neutral  fat.  In  this  way  the  fats  of  the  food 
are  rendered  available  for  the  nourishment  of  the  body. 

The  next  important  chemical  change  taking  place  in  the 
small  intestine  is  that  induced  by  the  amylopsin  of  the  pan- 
creatic juice,  which,  acting  in  essentially  the  same  manner  as 
the  ptyalin  of  saliva,  converts  any  unaltered  starch  into  dex- 
trins  and  sugar.  The  latter  substance,  maltose,  is  exposed 
to  the  action  of  another  enzyme  contained  in  the  intestinal 
secretion  termed  maltase,  which  transforms  it  into  dextrose, 
a  monosaccharide. 

In  these  ways  the  proteids,  fats,  and  carbohydrates  of  the 
food  are  gradually  digested,  so  far  as  conditions  will  admit, 
digestion  being  practically  completed  by  the  time  the  mate- 
rial reaches  the  ileoceecal  valve  at  the  beginning  of  the 
large  intestine.  Throughout  the  length  of  the  small  intes- 
tine absorption  proceeds  rapidly ;  water,  salts,  and  the  products 
of  digestion  passing  out  from  the  intestine  into  the  circulat- 
ing blood  and  lymph.  At  the  ileocsecal  valve,  however, 
the  contents  of  the  intestine  are  practically  as  fluid  as  at  the 
beginning  of  the  small  intestine,  due  to  the  fact  that  water 
is  continually  being  secreted  into  the  intestine.  In  the  large 
intestine,  the  contents  become  less  and  less  fluid  through 
reabsorption  of  the  water,  and  as  the  propulsive  movements 
of  the  circular  and  longitudinal  muscle  fibres  of  the  intestinal 
wall  carry  the  material  onward  toward  the  rectum,  the  last 
portions  of  available  nutriment  are  absorbed.  Finally,  in 
varying  degree,  certain  putrefactive  changes  are  observed  in 
the  large  intestine  involving  a  breaking  down  of  some  resid- 
ual proteid  matter,  through  the  agency  of  micro-organisms 
almost  invariably  present,  with  formation  of  such  substances 


38  THE  NUTRITION  OF  MAN 

as  indol,  skatol,  phenol,  fatty  acids,  etc.  These  processes, 
however,  in  health  are  held  rigidly  in  check,  and  count  for 
little  in  fitting  the  food  for  absorption.  Digestion,  on  the 
other  hand,  extending  as  we  have  seen  from  the  mouth  cavity 
to  the  ileocsecal  valve,  is  the  handmaiden  of  nutrition,  pre- 
paring all  three  classes  of  organic  foodstuffs  for  their  passage 
into  the  circulating  blood  and  lymph,  and  thus  paving  the 
way  for  their  utilization  by  the  hungry  tissue  cells. 


CHAPTER  II 

ABSORPTION,   ASSIMILATION,  AND   THE    PROCESSES 
OF  METABOLISM 

TOPICS:  Physiological  peculiarities  in  absorption.  Chemical  changes  in 
epithelial  walls  of  intestine.  Two  pathways  for  absorbed  material. 
Function  of  the  liver  as  a  regulator  of  carbohydrate.  Absorption  of 
proteid  products.  Assimilation  of  food  products.  Anabolism.  Ka- 
tabolism.  Metabolism.  Processes  of  metabolism.  Older  views  re- 
garding oxidation.  Discoveries  of  Lavoisier.  The  views  of  Liebig. 
Theory  of  luxus  consumption.  Oxidation  in  the  body  not  simple 
combustion.  Oxygen  not  the  cause  of  the  decompositions.  Oxidation 
not  confined  to  any  one  place.  Intracellular  enzymes.  Living  cells 
the  guiding  power  in  katabolism.  Some  intermediary  products  of 
tissue  metabolism.  Chemical  structure  of  different  proteids.  De- 
composition products  of  nucleoproteids.  Relation  to  uric  acid.  Action 
of  specific  intracellular  enzymes.  Creatin  and  creatinin.  Relation 
to  urea.  Proteid  katabolism  a  series  of  progressive  chemical  decompo- 
sitions. Intracellular  enzymes  as  the  active  agents. 

DIGESTION  being  completed,  and  the  available  portion 
of  the  foodstuffs  thereby  converted  into  forms  suitable 
for  absorption,  the  question  naturally  arises,  In  what  manner 
are  these  products  transported  from  the  alimentary  tract  to  the 
tissues  and  organs  of  the  body?  In  attempting  to  answer 
this  question,  we  shall  find  many  illustrations  of  the  precise 
and  undeviating  methods  which  prevail  in  the  processes  of 
nutrition.  For  example,  it  would  seem  plausible  to  assume 
that  the  different  forms  of  sugar  entering  into  man's  ordi- 
nary diet,  all  of  them  being  soluble,  would  be  directly  ab- 
sorbed and  at  once  utilized,  but  such  is  far  from  being  the 
case.  Milk-sugar  and  cane-sugar,  both  appearing  in  greater 


40  THE    NUTRITION  OF  MAN 

or  less  degree  in  our  daily  dietaries,  if  introduced  directly 
into  the  blood,  are  at  once  excreted  through  the  kidneys  un- 
changed. The  body  cannot  use  them,  and  they  are  gotten 
rid  of  as  speedily  as  possible,  much  as  if  they  were  poisons. 
When  taken  by  way  of  the  mouth,  however,  they  are  utilized, 
simply  because  in  the  intestine  two  enzymes  are  present  there, 
known  as  lactase  and  invertase,  which  break  each  of  the 
sugars  apart  into  two  smaller  molecules.  In  other  words, 
milk-sugar  and  cane-sugar  are  disaccharides,  and  if  they  are  to 
be  absorbed  in  forms  capable  of  being  made  use  of  by  the  body 
they  must  be  split  apart  into  simpler  sugars,  viz.,  monosac- 
charides,  such  as  dextrose,  levulose,  etc.  The  great  bulk 
of  the  carbohydrate  food  consumed  by  man  is  in  the  form  of 
starch,  and  this,  as  we  have  seen,  is  converted  into  maltose 
by  the  action  of  saliva  and  pancreatic  juice.  Maltose,  how- 
ever, like  cane-sugar,  is  a  disaccharide,  and  the  body  has  no 
power  to  burn  it  or  utilize  it  directly ;  but  in  the  intestine 
and  elsewhere  is  an  enzyme  termed  maltase,  which  breaks 
up  maltose  into  two  molecules  of  the  monosaccharide  dex- 
trose, and  this  the  body  can  use.  Man  frequently  consumes 
starch  to  the  extent  of  a  pound  a  day,  and  if  utilized  it  must 
all  undergo  transformation  into  maltose,  and  then  into  dex- 
trose. There  is  no  apparent  reason  why  maltose  should  not 
be  absorbed  and  assimilated  as  readily  as  dextrose,  but  so 
urgent  is  the  necessity  for  this  conversion  into  dextrose  that 
in  the  blood  itself  there  is  present  maltase,  to  effect  the  trans- 
formation of  any  maltose  that  may  gain  entrance  there.  We 
are  here  face  to  face  with  a  simple  fact  in  nutrition.  The 
body  cannot  utilize  disaccharides  directly.  Why  it  is  so  we 
cannot  say,  but  the  fact  is  a  good  illustration  of  the  prin- 
ciple that  nothing  can  be  taken  for  granted  in  our  study  of 
nutrition. 

For  years,  physiologists  assumed  that  the  ordinary  physical 
laws  of  osmosis,  imbibition,   and  diffusion  were  quite  ade- 


ABSORPTION,    ASSIMILATION,   METABOLISM      41 

quate  to  explain  the  passage  of  digested  food  materials  into 
the  blood  and  lymph.  If  a  substance  was  soluble  and  diffu- 
sible, that  was  sufficient ;  it  w-ould  quite  naturally  be  absorbed 
in  harmony  with  its  diffusion  velocity.  This,  however,  is 
not  wholly  true,  since  experiment  shows  that  the  rapidity  of 
absorption  of  diffusible  substances  through  the  wall  of  the 
intestine  is  by  no  means  always  proportional  to  the  diffu- 
sion velocity  of  the  substance.  The  lining  membrane  of  the 
small  intestine,  where  absorption  mainly  takes  place,  is  not 
to  be  compared  to  a  dead  parchment  membrane.  On  the 
contrary,  it  is  made  up  of  living  protoplasmic  cells ;  absorp- 
tion is  not  a  physical,  but  a  physiological,  process,  in  which 
the  living  epithelium  cells  stand  as  guardians  of  the  portals, 
ready  to  challenge  and,  if  need  be,  modify  the  rate  of  pas- 
sage. Osmosis  and  diffusion  undoubtedly  play  some  part  in 
absorption,  but  they  alone  are  not  sufficient  to  account  for 
what  actually  takes  place  in  the  absorption  of  digestion 
products,  and  other  substances  from  the  living  intestine. 

The  primary  products  formed  in  the  digestion  of  proteid 
foods  —  the  proteoses  and  peptones  —  afford  another  illustra- 
tion of  physiological  peculiarity  in  absorption.  These  bodies 
are  readily  soluble  and  quite  diffusible,  yet  they  are  never 
found  to  any  extent  in  the  circulating  blood  and  lymph  dur- 
ing health.  It  is  of  course  possible,  as  has  been  previously 
suggested,  that  as  soon  as  formed  they  undergo  transforma- 
tion into  simpler  decomposition  products  in  the  small  in- 
testine; but  this  is  by  no  means  certain.  If  proteoses  and 
peptones  are  injected  directly  into  the  blood,  they  cause  a 
marked  disturbance,  influencing  at  once  blood-pressure,  affect- 
ing the  coagulability  of  the  blood,  and  in  many  other  ways 
exhibiting  a  pronounced  deleterious  action  which  at  once  in- 
dicates they  are  out  of  their  normal  environment.  They  are 
not  at  home  in  the  circulating  blood,  and  the  latter  medium 
gets  rid  of  them  as  speedily  as  possible;  they  behave  like 


42  THE  NUTBITION  OF  MAN 

veritable  poisons,  and  yet  they  are  the  primary  products 
formed  in  the  digestion  of  all  proteid  foodstuffs.  On  the 
basis  of  all  physical  laws  governing  diffusion  they  should  be 
absorbed,  and  help  to  renew  the  proteids  of  the  blood  and 
later  the  proteids  of  the  tissues.  Yet,  as  we  have  said,  they 
are  not  normally  present  in  the  blood  or  lymph.  Apparently, 
in  the  very  act  of  absorption,  as  they  pass  through  the  epithe- 
lial cells  of  the  intestinal  wall,  before  they  gain  entrance  to 
the  blood  stream,  they  undergo  transformation  into  serum- 
albumin  and  globulin,  the  characteristic  blood  proteids.  The 
other  alternative  is  that,  as  previously  mentioned,  they  are 
completely  broken  down  in  the  intestine  into  amino-acids, 
etc.,  and  these  simpler  products  synthesized,  as  they  pass 
through  the  intestinal  wall  toward  the  blood,  into  serum- 
albumin  and  globulin.  Certainly  as  yet,  there  is  no  evidence 
that  the  amino-acids,  as  such,  go  through  the  epithelial  cells 
of  the  intestine ;  they  are  not  found  in  the  blood  or  lymph  to 
any  appreciable  extent,  yet  the  proteids  of  the  blood  are  re- 
inforced in  some  manner  by  the  products  of  proteid  digestion. 
Whichever  view  is  correct,  one  thing  is  perfectly  obvious, 
viz.,  that  in  the  act  of  absorption  the  products  resulting  from 
the  gastric  and  pancreatic  digestion  of  proteid  foods  are  ex- 
posed to  some  influence,  presumably  in  the  epithelial  cells 
of  the  intestinal  wall,  by  which  there  is  a  reconstruction  of 
proteid.  Further,  the  proteid  substances  so  formed  are  of  the 
type  peculiar  to  the  blood  of  that  particular  species  of  animal. 
The  proteids  of  beef,  mutton,  chicken,  oatmeal,  or  bread  go 
to  make  the  proteids  of  human  blood. 

From  these  statements,  it  is  obvious  that  what  we  term  ab- 
sorption is  something  more  than  a  simple  diffusion  of  soluble 
substances  from  the  alimentary  tract  into  the  blood  current. 
The  process  is  much  more  complex  than  appears  on  the  sur- 
face, and  our  lack  of  definite  knowledge,  in  spite  of  numerous 
efforts  to  unravel  the  mystery,  merely  strengthens  the  view 


ABSOBPTION,  ASSIMILATION,  METABOLISM      43 

that  we  are  dealing  here  with  an  obscure  physiological  problem, 
and  not  a  simple  physical  one.  Digestion  induces  a  splitting 
up  of  the  food  proteid  into  fragments,  large  or  small,  while 
incidental  to  absorption  there  is  apparently  a  reconstruction, 
or  synthesis,  of  proteid  from  the  fragments  so  formed.  The 
process  seems  somewhat  costly,  physiologically  speaking,  yet 
when  one  considers  the  variety  of  proteids  consumed  as  food, 
it  is  easy  to  comprehend  how  essential  it  is  that  in  some 
manner,  as  in  absorption,  there  be  opportunity  for  construc- 
tion of  the  specific  proteids  of  the  blood  and  lymph. 

We  find  an  analogous  process  in  the  absorption  of  fats. 
As  we  have  seen,  the  fats  of  the  food  are  broken  apart  in  the 
small  intestine  into  glycerin  and  free  fatty  acid,  a  portion 
of  the  latter,  and  perhaps  all,  combining  with  the  alkali  of  the 
intestinal  juices  to  form  soluble  soaps,  or  sodium  salts  of  the 
respective  fatty  acids.  The  neutral  fats  present  in  animal 
and  vegetable  foods  are  all  alike  in  containing  the  glyceryl 
radicle,  but  they  differ  in  the  character  of  the  fatty  acids 
present.  Further,  one  form  of  animal  fat,  like  that  from  beef, 
may  contain  quite  a  different  proportion  of  stearin,  palmitin, 
and  olein  than  is  present  in  the  fat  of  another  animal,  like 
mutton.  By  digestion,  however,  they  are  all  broken  apart 
into  fatty  acid  and  glycerin.  These  acids  and  their  salts  can 
be  readily  detected  in  the  intestine,  but  they  are  not  found 
in  the  blood  or  lymph,  yet  shortly  after  fatty  food  is  taken 
the  lymph  is  seen  to  be  milky  from  fat.  Obviously,  the  fatty 
acids  liberated  in  the  intestine  are  absorbed,  either  as  soluble 
soaps  or  as  free  fatty  acids  dissolved  in  bile,  but  as  they  pass 
through  the  epithelial  cells  of  the  intestine  into  the  lacteal 
radicles,  there  is  a  synthesis  or  reconstruction  of  fat;  and  as 
a  result,  neutral  fats  and  not  soaps  are  found  in  the  lymph. 
Here,  then,  we  have  a  process  quite  analogous  to  what  ap- 
parently occurs  in  the  absorption  of  proteid,  though  less  com- 
plex ;  and  it  is  possible  that  this  is  one  of  the  factors  which 


44  THE  NUTRITION  OF  MAN 

aids  in  the  formation  of  a  specific  fat  mixture  corresponding, 
in  a  measure,  to  the  type  of  fat  present  in  the  particular  spe- 
cies. It  is  well  understood  that  the  fat  of  an  animal's  tissues 
may  be  modified  somewhat  by  the  character  of  the  fat  fed,  yet 
in  spite  of  this  there  is  a  certain  degree  of  constancy  in  com- 
position which  calls  for  explanation.  Sheep  and  oxen  feed- 
ing in  the  same  pasture  have  fat  widely  different  in  the 
proportion  of  stearin,  palmitin,  etc.  The  fat  of  man's  tissues 
is  fairly  definite  in  composition,  yet  he  eats  a  great  variety  of 
fatty  foods.  One  man  may  consume  large  amounts  of  hard 
mutton  fat  with  its  relatively  large  content  of  stearin,  while 
another  individual  may  take  his  fat  mainly  in  the  form  of  the 
soft  butter  fats,  with  their  relatively  large  content  of  olein 
and  palmitin.  In  both  cases,  the  fat  of  the  man's  tissues  will 
be  essentially  the  same.  To  be  sure,  the  changes  that  take 
place  in  the  tissue  cells,  reinforced  by  the  construction  of 
fat  from  other  sources,  may  be  partly  responsible  for  this 
constancy  of  composition,  but  the  transformations  incidental 
to  absorption  are  quite  possibly,  in  some  measure,  helpful 
thereto. 

The  great  bulk  of  the  digested  food  material  is  absorbed 
from  the  small  intestine,  and  there  are  two  pathways  open 
through  which  the  absorbed  material  can  gain  access  to  the 
blood.  The  one  path  leads  directly  to  the  liver,  and  sub- 
stances taking  this  course  are  exposed  to  the  action  of  this 
organ,  before  they  enter  into  the  general  circulation.  The 
other  path  is  through  the  lacteal  or  lymphatic  system,  and 
constitutes  a  roundabout  way  for  substances  to  enter  the 
blood  stream,  since  they  must  first  pass  through  the  thoracic 
duct  before  entering  the  main  circulation.  As  a  general 
truth,  it  may  be  stated  that  fats  are  absorbed  through  the 
latter  channel,  while  carbohydrates  and  proteids  follow  the 
first  path.  The  innumerable  blood  capillaries  in  the  villi  of 
the  intestine  take  up  the  products  resulting  from  the  diges- 


ABSORPTION,  ASSIMILATION,   METABOLISM      45 

tion  of  proteids  and  carbohydrates,  through  which  they  are 
passed  into  the  portal  vein,  and  thereby  distributed  through- 
out the  liver.  This  means  that  both  carbohydrates  and  pro- 
teids —  or  their  decomposition  products  —  are  exposed  to  a 
variety  of  possible  changes  in  this  large  glandular  organ, 
before  they  can  enter  into  the  tissues  of  the  body.  As  we 
have  seen,  practically  all  carbohydrate  food  is  converted  into 
a  monosaccharide,  principally  dextrose,  in  the  alimentary 
tract;  and  it  is  in  this  form  of  a  simple  sugar  that  the  car- 
bohydrate passes  into  the  blood.  This  might  easily  mean  a 
pound  of  sugar  absorbed  during  the  twenty-four  hours,  and 
would  obviously  give  to  the  blood  a  high  degree  of  concen- 
tration, unless  the  excess  was  quickly  disposed  of.  Sugar  is 
very  diffusible,  and  if  it  accumulates  to  any  extent  in  the 
blood  it  is  quickly  gotten  rid  of  by  excretion  through  the 
kidneys.  This,  however,  is  wasteful,  physiologically  and 
otherwise,  and  does  not  ordinarily  occur  except  in  diseased 
conditions.  Further,  physiologists  have  learned  that  a  cer- 
tain small,  but  definite,  amount  of  sugar  in  the  blood  is  a 
necessary  requirement  in  nutrition,  and  it  is  the  function  of 
the  liver  to  maintain  the  proper  carbohydrate  level. 

We  must  again  emphasize  the  great  importance  of  carbo- 
hydrate food;  there  is  a  far  larger  amount  of  starchy  food 
consumed  than  of  any  other  foodstuff,  and  it  is  more  readily 
available  as  a  source  of  energy.  Its  presence  in  the  blood, 
in  the  form  of  sugar,  is  constantly  demanded,  but  it  must  be 
kept  within  the  proper  limits  for  the  uses  of  the  different 
tissues  and  organs  of  the  body.  The  liver  serves  as  an  effect- 
ive regulator,  maintaining,  in  spite  of  all  fluctuations  in  the 
supply  and  demand,  a  definite  percentage  of  sugar  such  as  is 
best  adapted  to  keep  the  tissues  of  the  body  in  a  normal  and 
healthy  condition.  This  regulation  by  the  liver  is  rendered 
possible  through  the  ability  of  the  hepatic  cells  to  transform 
the  sugar  brought  to  the  gland  into  glycogen,  so-called  animal 


46  THE  NUTEITION  OF  MAN 

starch,  which  is  stored  up  in  the  liver  until  such  time  as  it  is 
needed  by  the  body.     The  process  is  one  of  dehydration,  the 
reverse  of  what  takes  place  in  the  intestine  when  ordinary 
starch  is  converted  into  maltose  and  dextrose.     The  efficiency 
of  this  regulating  mechanism  depends  also  upon  the  ability  of 
the  liver  to  transform  glycogen  into  sugar,  presumably  through 
the  agency  of  an  enzyme  in  the  hepatic  cells.     Hence,  glyco- 
gen may  be  looked  upon  as  a  temporary  reserve  supply  of 
carbohydrate,  manufactured  and  stored  in  the  liver  during 
digestion,  when  naturally  large  amounts  of  sugar  are  passing 
into  the  portal  blood,  and  to  be  drawn  upon  whenever  from 
any  cause  the  content  of  sugar  in  the  blood   threatens  to 
fall  below  normal.     Obviously,  there  must  be  some  delicate 
machinery  for  the  adjustment  of  these  opposite  changes  in 
the  liver,  and  we  may  well  believe  that  it  is  associated  with 
the  composition  of  the  blood  itself,  which  in  some  fashion 
stimulates  and  inhibits,  as  may  be  required,  the  functional 
activity  of  the  liver,  or  its  component  cells.     In  any  event, 
we  have  in  this  so-called  glycogenic  function  of  the  liver  a 
most  effective  means  for  accomplishing   the  complete   and 
judicious  utilization  of  all  the  sugar  formed  from  the  carbo- 
hydrates of  the  food,  after  it  has  once  passed  beyond  the  con- 
fines of  the  alimentary  tract  into  the  blood;  preventing  all 
loss,  and  at  the  same  time  guarding  against  all  danger,  from 
undue  accumulation  of  sugar  in  the  circulation.     We  see, 
too,  how  wise  the  provision  that  all  sugar  should  pass  from 
the  alimentary  canal  into  the  portal  circulation  and  not  by 
way  of  the  lymphatics,  since  by  the  latter  channel  the  regulat- 
ing action  of  the  liver  would  be  mainly  lost.     Further,  recall- 
ing how  soluble  and  diffusible  sugar  is,  we  may  well  marvel 
that  it  practically  all  passes  from  the  intestine  by  way  of  the 
blood,   and  escapes  entry  into  the  lymphatics.     Surely,  this 
marked  shunning  of  the  other  equally  accessible   pathway 
affords  a  striking   illustration   of  selective  Action  such   as 


ABSORPTION,  ASSIMILATION,   METABOLISM      47 

might  be  expected  in  a  physiological  process,  but  not  in  har- 
mony with  the  ordinary  physical  laws  of  osmosis  or  diffusion. 
In  conformity  with  this  statement,  it  may  be  mentioned  that 
appropriate  experiments  have  clearly  demonstrated  that  the 
different  sugars  available  as  food  are  not  absorbed  from  the 
intestine  in  harmony  with  their  diffusion  velocity,  but  show 
deviations  therefrom  which  can  be  explained  only  on  the 
ground  that  the  intestinal  wall  exercises  some  selective  action, 
due  to  the  living  cells  composing  it.  Likewise  interesting  in 
their  bearing  on  nutrition  are  the  observations  of  Hofmeister,1 
who  finds  by  experiments  on  dogs  that  the  assimilation  limit 
of  the  different  sugars  shows  marked  variation.  Thus,  dex- 
trose, levulose,  and  cane-sugar  have  the  highest  assimilation, 
while  milk-sugar  is  far  less  easily  and  completely  assimilated. 
If  this  is  equally  true  of  man,  it  indicates  that  starchy  foods, 
with  their  ultimate  conversion  into  dextrose,  are  to  be  ranked 
as  having  a  high  assimilation  limit,  thus  affording  additional 
evidence  of  their  high  nutritive  value. 

In  the  absorption  of  proteid  products,  their  passage  from 
the  intestine  by  way  of  the  portal  circulation  insures  expo- 
sure to  the  action  of  the  hepatic  cells,  before  they  are  distrib- 
uted by  the  general  circulation  throughout  the  body.  It  is 
only  under  conditions  of  an  excessive  intake  of  proteid  foods 
that  their  products  are  absorbed  by  way  of  the  lymphatics. 
These  points  are  clearly  established,  and  there  is  every  ground 
for  believing  that  substantial  reasons  exist  to  account  for  this 
single  line  of  departure.  Just  what  the  liver  does,  however, 
is  uncertain.  In  fact,  as  already  indicated,  there  is  lack  of 
definite  knowledge  as  to  how  far  the  proteid  foods  are  broken 
down  in  digestion,  prior  to  absorption.  The  combined  action 
of  pepsin,  trypsin,  and  erepsin,  if  sufficiently  long  continued, 
can  accomplish  a  complete  disruption  of  the  proteid  molecule. 

1  Franz  Hofmeister:  Ueber  Resorption  und  Assimilation  der  NahrstofEe. 
Archiv  f.  d.  exper.  Pathol.  u.  Pharm.,  Band  25,  p.  240. 


48  THE  NUTRITION   OF  MAN 

We  are  inclined  to  assume  in  a  general  way  that  the  "  proteids 
taken  as  food  cannot  find  a  place  in  the  economy  of  the 
animal  body  till  they  have  been,  as  it  were,  melted  down  and 
recast."  1  How  far  this  melting  down  or  disruption  extends 
in  normal  digestion,  we  do  not  at  present  know.  As  already 
stated,  neither  proteoses  and  peptones,  nor  the  amino-acids,  are 
found  in  the  blood  stream  in  sufficient  amounts,  or  with  that 
frequency,  to  suggest  absorption  in  these  forms.  Possibly,  as 
some  physiologists  have  suggested,  the  amount  of  any  of  these 
products  to  be  found  at  any  one  time  in  a  given  quantity  of 
blood  is  too  small  for  certain  recognition,  yet  in  the  twenty- 
four  hours  the  amount  passing  from  intestine  to  liver  might  be 
sufficiently  large  to  equal  the  total  proteid  absorbed.  We  can, 
however,  at  present  only  conjecture,  and  must  rest  content 
with  the  simple  statement  that  in  the  digestion  of  the  pro- 
teid foodstuffs,  proteoses,  peptones,  and  amino-acids  are 
formed,  and  that  by  transformation  or  total  reconstruction  of 
these  products,  special  types  of  proteid  are  manufactured 
either  in  the  epithelial  cells  of  the  intestinal  walls  during 
absorption,  or  elsewhere  in  the  body  after  absorption.  If  this 
latter  is  the  case,  the  liver  might  readily  be  regarded  as  a 
likely  spot  for  the  synthesis  to  occur. 

Bearing  in  mind  what  has  been  said  regarding  the  produc- 
tion of  specific  types  of  proteid  by  every  species  of  animal, 
we  can  the  more  readily  conceive  of  a  synthesis  "out  of 
fragments  of  the  original  molecules  rearranged  and  put  to- 
gether in  new  combinations,  by  processes  in  which  the  intes- 
tine can  hardly  be  supposed  to  play  a  part."  This,  the  liver 
might  well  be  assumed  as  capable  of  accomplishing,  and  if 
we  were  disposed  to  accept  this  view  we  might  use  as  an 
argument  the  fact  that  the  products  of  proteid  digestion 
are  taken  directly  to  this  organ,  before  being  cast  loose  in 

1  J.  B.  Leathes :  Problems  in  Animal  Metabolism.  Blakiston's  Son  and  Co., 
1906,  p.  123. 


ABSORPTION,   ASSIMILATION,   METABOLISM     49 

the  tissues  and  organs  of  the  body.  There  is  perhaps  as 
good  ground  for  assuming  that  a  synthesis  or  reconstruc- 
tion of  proteid  takes  place  all  over  the  body;  that,  as  sug- 
gested by  Leathes,  "the  synthesis  of  proteids  is  a  function 
of  every  cell  in  the  body,  each  one  for  itself,  and  that  the 
material  out  of  which  all  proteids  in  the  body  are  made  is 
not  proteid  in  any  form,  but  the  fragments  derived  from 
proteids  by  hydrolysis,  probably  the  amido-acids,  which  in 
different  combinations  and  different  proportions  are  found 
in  all  proteids,  and  into  which  they  are  all  resolved  by  the 
processes,  autolytic  or  digestive,  which  can  be  carried  out 
in  every  cell  in  the  body."  It  is  certainly  a  reasonable 
hypothesis,  and  since  we  lack  positive  knowledge  it  cannot 
at  present  be  disproved.  All  that  we  can  affirm  in  the  light 
of  established  fact  is  that  the  products  of  proteid  digestion  are 
absorbed  from  the  intestine  by  way  of  the  portal  circulation, 
and  that  either  in  their  passage  through  the  intestinal  wall, 
or  later  on  in  the  liver  or  elsewhere,  there  is  a  construction 
of  new  proteid  to  meet  the  wants  of  the  body.  The  liver, 
indeed,  may  be  effective  in  both  construction  and  destruc- 
tion of  proteid,  but  there  is  no  way  of  telling  at  present  just 
how  far  it  acts  in  either  direction. 

Regarding  the  absorption  of  fats,  a  single  statement  will 
suffice,  in  addition  to  what  has  already  been  said.  Fats  gain 
access  to  the  general  circulation  by  passing  from  the  intestine 
into  the  lacteal  radicles,  thence  into  the  lymphatics,  whence 
they  move  onward  into  the  thoracic  duct,  and  from  there  are 
emptied  into  the  great  veins  at  the  neck.  A  small  amount 
is  apparently  absorbed  in  the  form  of  soap  by  the  portal  cir- 
culation, but  by  far  the  larger  amount  of  fat  gains  access  to 
the  blood  stream  without  going  through  the  liver. 

In  these  ways,  the  blood  and  lymph  are  continually  sup- 
plied with  proteid,  fat,  and  carbohydrate  from  the  ingested 

4 


50  THE  NUTRITION   OF  MAN 

food,  and  as  these  fluids  surround  and  permeate  the  organ- 
ized elements  of  the  tissues,  the  latter  are  enabled  to  gain 
what  they  need  to  maintain  their  nutritive  balance.  Living 
matter  is  essentially  unstable;  it  is  the  seat  of  chemical 
changes  of  various  kinds,  anabolic  or  constructive,  and  kata- 
bolic  or  destructive.  The  more  comprehensive  term  "  meta- 
bolic "  is  applied  to  all  of  these  changes  that  take  place  in 
living  matter.  In  anabolism,  the  dead,  inert  proteids,  fats, 
and  carbohydrates  are  more  or  less  assimilated  and  made  a 
part  of  the  living  matter  of  the  tissue  cells,  while  at  the  same 
time  a  certain  amount  of  the  food  material,  probably  the 
larger  amount,  is  simply  stored  as  such,  or  left  to  circulate  in 
the  blood  and  lymph,  without  being  raised  to  the  higher  level 
of  living  protoplasm.  In  katabolism,  this  accumulated  mate- 
rial, and  in  some  degree  the  living  substance  itself,  is  broken 
down  or  disintegrated  with  liberation  of  the  stored-up  energy, 
which  manifests  itself  in  the  form  of  heat  and  mechanical 
work.  At  times,  the  anabolic  processes  predominate  and 
there  is  a  relatively  large  accumulation  of  stored-up  materials ; 
while  at  other  times,  katabolism,  with  its  attendant  chemical 
decompositions,  predominates,  and  the  body  loses  correspond- 
ingly. The  point  to  be  emphasized  here  is  that  the  living 
body,  with  its  multitude  of  living  cells,  is  the  seat  of  inces- 
sant change.  Construction  and  destruction  are  continually 
going  forward  side  by  side ;  sometimes  the  one  and  sometimes 
the  other  predominating,  according  to  existing  conditions. 
The  living  protoplasm  with  its  attendant  storage  material  is, 
under  ordinary  conditions,  constantly  being  made  good  from 
the  assimilated  food,  a  part  of  which  is  raised  to  the  dignity 
of  living  matter  and  becomes  an  integral  part  of  the  living 
cells,  while  the  larger  portion  is  simply  stored  for  future 
uses,  or  circulates  in  the  blood  and  lymph  which  bathe  them. 
Doubtless,  this  storage  or  circulating  material  is  the  main 
source  of  the  energy  which  constantly  flows  from  the  cells 


ABSORPTION,  ASSIMILATION,   METABOLISM      51 

in  the  form  of  heat  and  of  work,  as  a  result  of  the  disruptive 
changes  that  constitute  katabolism. 

Worthy  of  special  notice  is  the  fact  that  cell  protoplasm 
is  essentially  proteid  in  nature;  water  and  proteid  make 
up  the  larger  part  of  its  substance,  to  which  are  added 
small  proportions  of  carbohydrate,  fat,  and  mineral  matter. 
Proteid  is  the  basis  of  cell  protoplasm;  it  is  the  chemical 
nucleus  of  living  matter,  and  owing  to  the  large  size  of 
its  molecule,  with  its  large  number  of  contained  atoms,  is 
capable  of  many  combinations  and  many  alterations.  Most 
of  the  reactions  characteristic  of  katabolism  centre  around 
this  proteid,  but  the  disruptive  changes  that  occur  undoubt- 
edly involve  more  largely  the  circulating  materials  present 
in  the  blood  and  lymph,  and  which  bathe  the  cells,  rather 
than  the  so-called  fixed,  or  organ  proteid,  of  the  cell  sub- 
stance itself.  Still,  while  the  circulating  blood  and  lymph 
furnish  largely  the  substances  which  are  made  to  undergo 
disintegration  in  katabolism,  the  living  protoplasmic  cell  is 
the  controlling  power  which  regulates  the  extent  and  char- 
acter of  the  decompositions,  and  proteid  matter  is  the  chemi- 
cal basis  of  protoplasm.  From  these  statements,  we  again 
have  suggested  the  significant  importance  of  the  proteid  foods 
in  nutrition,  since  they  alone  can  furnish  the  material  which 
constitutes  the  chemical  basis  of  living  cells.  The  human 
body,  which  represents  the  highest  form  of  animal  life,  is 
merely,  as  stated  by  another,  "  literally  a  nation  of  cells  de- 
rived from  a  single  cell  called  the  ovum,  living  together,  but 
dividing  the  work,  transformed  variously  into  tissues  and 
organs,  and  variously  surrounded  by  protoplasm  products  " 
(Waller). 

The  processes  involved  in  metabolism  are  not  easily  un- 
ravelled. The  word  itself  is  simple,  but  it  is  employed  to 
designate  that  complex  of  "  chemical  changes  in  living  organ- 
isms which  constitute  their  life,  the  changes  by  which  their 


52  THE  NUTRITION  OF  MAN 

food  is  assimilated  and  becomes  part  of  them,  the  changes 
which  it  undergoes  while  it  shares  their  life,  and  finally  those 
by  which  it  is  returned  to  the  condition  of  inanimate  matter. 
Gathered  together  under  this  one  phrase  are  some  of  the  most 
intricate  and  inaccessible  of  natural  phenomena.  It  implies 
also,  and  gently  insists  on  the  idea,  that  all  the  phenomena 
of  life  are  at  bottom  chemical  reactions  "  (Leathes).  Re- 
garding the  processes  of  anabolism,  as  in  the  construction  of 
living  protoplasm  out  of  inert  food  materials,  we  can  say 
nothing.  This  is  altogether  beyond  our  ken  at  present,  and 
doubtless  will  remain  so,  since  it  involves  a  chemical  altera- 
tion, or  change,  akin  to  that  of  bringing  the  dead  to  life.  With 
the  processes  of  katabolism,  however,  we  may  hope  for  more 
satisfactory  results;  and,  indeed,  to-day  we  have  consider- 
able information  of  value  as  to  some  of  the  methods,  at  least, 
which  are  the  cause  of  this  phase  of  nutrition.  This  knowl- 
edge, however,  has  been  slow  of  attainment. 

In  the  earlier  years  of  the  sixteenth  century,  when  anatomy 
and  physiology  were  beginning  to  make  progress,  the  savants 
of  that  day,  hampered  as  they  were  by  grave  misconceptions 
and  by  the  lack  of  any  understanding  of  chemical  phenomena, 
could  not  take  advantage,  naturally,  of  the  suggestion  that  as 
wood  burns  or  oxidizes  in  the  air  with  liberation  of  heat,  so 
might  the  food  substances,  absorbed  by  the  body,  undergo 
oxidation  in  the  tissues  and  thus  give  rise  to  animal  heat. 
Such  suggestions  were  at  that  time  as  a  closed  book,  and  so 
we  find  Vesalius,  in  1543,  teaching  the  Galenic  doctrines  in 
physiology  then  prevalent.  The  conception  of  heat  produc- 
tion, as  it  existed  at  that  time,  may  be  inferred  from  the  fol- 
lowing quotation:1  "The  parts  of  the  food  absorbed  from 
the  alimentary  canal  are  carried  by  the  portal  blood  to  the 


1  Taken  from  Sir  Michael  Foster's  "  Lectures  on  the  History  of  Physiology 
during  the  Sixteenth,  Seventeenth,  and  Eighteenth  Centuries."  Cambridge, 
1901,  p.  12. 


ABSORPTION,   ASSIMILATION,   METABOLISM      53 

liver,  and  by  the  influence  of  that  great  organ  are  converted 
into  blood.  The  blood  thus  enriched  by  the  food  is  by  the 
same  great  organ  endued  with  the  nutritive  properties  summed 
up  in  the  phrase  '  natural  spirits. '  But  blood  thus  endowed 
with  natural  spirits  is  still  crude  blood,  unfitted  for  the 
higher  purposes  of  the  blood  in  the  body.  Carried  from  the 
liver  by  the  vena  cava  to  the  right  side  of  the  heart,  some  of 
it  passes  from  the  right  ventricle  through  innumerable  invisi- 
ble pores  in  the  septum  to  the  left  ventricle.  As  the  heart 
expands  it  draws  from  the  lungs  through  the  vein-like  artery 
air  into  the  left  ventricle.  And  in  that  left  cavity,  the  blood 
which  has  come  through  the  septum  is  mixed  with  the  air 
thus  drawn  in,  and  by  the  help  of  that  heat,  which  is  innate 
in  the  heart,  which  was  placed  there  as  the  source  of  the  heat 
of  the  body  by  God  in  the  beginning  of  life,  and  which  re- 
mains there  until  death,  is  imbued  with  further  qualities,  is 
laden  with  '  vital  spirits, '  and  so  fitted  for  its  higher  duties. 
The  air  thus  drawn  into  the  left  heart  by  the  pulmonary  vein, 
at  the  same  time  tempers  the  innate  heat  of  the  heart  and 
prevents  it  from  becoming  excessive."  In  other  words,  heat 
was  considered  as  a  divine  gift,  and  as  can  readily  be  seen, 
there  was  an  utter  lack  of  appreciation  of  the  use  of  air  in 
breathing.  Even  van  Helmont,  who  lived  in  1577-1644, 
and  was  in  a  sense  an  alchemist,  still  gave  credence  to  the 
spirits,  viz.,  that  the  food  absorbed  from  the  stomach  and 
intestine  is  in  the  liver  endued  with  natural  spirits,  while  in 
the  heart  the  natural  spirits  are  converted  into  vital  spirits, 
and  in  the  brain  the  vital  spirits  are  transformed  into  animal 
spirits.1  Later,  Malpighi  discovered  the  true  structure  of 
the  lungs,  and  Borelli,  in  1680,  exposed  the  erroneous  views 
then  prevalent  regarding  the  purpose  of  breathing.  It  is  not 
true,  says  Borelli,  that  the  use  of  breathing  is  to  cool  the  ex- 


1  See  Foster's  Lectures,  p.  136. 


54  THE  NUTRITION  OF  MAN 

cessive  heat  of  the  heart  or  to  ventilate  the  vital  flame,  but 
we  must  believe  that  this  great  machinery  of  the  lungs,  with 
their  accompanying  blood  vessels,  is  for  some  grand  purpose. 
In  a  long  and  vigorous  argument,  he  contends  that  the  "air 
taken  in  by  breathing  is  the  chief  cause  of  the  life  of  animals, 
far  more  essential  than  the  working  of  the  heart  and  the  cir- 
culation of  the  blood."  He  quotes  the  experiments  of  Boyle, 
who  showed  in  1660  "  that  even  in  a  partial  vacuum  brought 
about  by  his  air  pump,  flame  was  extinguished  and  life  soon 
came  to  an  end ;  the  candle  went  out  and  the  mouse  or  the 
sparrow  died." 

At  this  time,  and  for  long  afterwards,  the  belief  was  preva- 
lent that  the  air  taken  up  by  the  blood  in  the  lungs  was 
the  air  of  the  atmosphere  in  its  entirety.  No  one  appears  to 
have  thought  of  the  possibility  of  only  a  part  of  the  air  being 
used,  for  at  that  time  there  was  no  suspicion  that  air  was  a 
mixture  of  substances.  Mayow,  however,  in  1668,  showed 
that  it  was  not  the  whole  air  which  was  employed  for  respira- 
tion, but  a  particular  part  only.  At  this  time,  great  attention 
was  being  given  to  a  study  of  nitre  or  saltpetre;  its  won- 
derful properties  in  combustion  were  being  recognized,  and 
Mayow,  who  was  a  chemist  of  repute,  claimed  that  it  had  its 
origin  partly  in  the  air  and  partly  in  the  earth.  The  air 
"  which  surrounds  us,  and  which,  since  by  its  tenuity  escapes 
the  sharpness  of  our  eyes,  seems  to  those  who  think  about 
it  to  be  an  empty  space,  is  impregnated  with  a  certain  uni- 
versal salt,  of  a  nitro-saline  nature,  that  is  to  say,  with  a 
vital,  fiery,  and  in  the  highest  degree  fermentative  spirit,"  to 
which  the  name  of  "  igneo-aereus  "  was  applied.  Nitre  was 
shown  to  be  composed  of  a  sal  fixum  or  sal  alkali,  —  potash  as 
it  is  now  called,  —  and  was  obviously  derived  from  the  earth, 
while  the  other  part  of  nitre  was  made  up  of  the  spiritus 
acidus,  or  nitric  acid.  For  a  time  it  was  supposed  that  the 
whole  of  this  spiritus  acidus  was  contained  in  the  atinos- 


ABSORPTION,    ASSIMILATION,  METABOLISM      55 

phere,  but  it  was  soon  recognized  that  this  could  not  be  the 
case,  since  nitric  acid  was  found  to  be  a  corrosive  liquid,  de- 
structive to  life  and  quite  incapable  of  supporting  combus- 
tion.    Hence,  Mayow  concluded  that  only  a  part  of  the  acid 
exists  in  the  atmosphere,   viz.,  that  part  which  he  termed 
spiritus  nitro-aereus.     In  combustion,  there  is  something  in 
the  air  which  is  necessary  for  the   burning  of  every  flame, 
unless   perchance  igneo-aereal  particles  should  pre-exist  in 
the  thing  to  be   burnt.     These   igneo-aereal   particles  form 
"  the  more  active  and  subtle  part  of  air  which  is  thus  neces- 
sary for  combustion,  exist  in  nitre  and  indeed  constitute  its 
'  more  active  and  fiery  part. ' '      Mayow  fully  recognized  that 
burning  and  breathing  involved  in  a  measure  the  same  process ; 
both  consisted  in  the  consumption  of  the  igneo-aereal  parti- 
cles present  in  the  air.     "If  a  small  animal  and  a  lighted 
candle  be  shut  up  in  the  same  vessel,  the  entrance  into  which 
of  air  from  without  be  prevented,  you  will  see  in  a  short 
time  the  candle  go  out,  nor  will  the  animal  long  survive  its 
funeral  torch.     Indeed,  [says  Mayow]  I  have  found  by  ob- 
servation that  an  animal  shut  up  in  a  flask  together  with 
a  candle  will  continue  to  breathe  for  not  much  more  than 
half  the  time  than  it  otherwise  would,  that  is,  without  the 
candle."     Something   contained   in   the   air,  necessary  alike 
for  supporting   combustion   and   for  sustaining  life,  passes 
from  the  air  into  the  blood.     Mayow  expressed  his  thoughts 
in  these  words :  "  And  indeed  it  is  very  probable  that  certain 
particles   of   a   nitro-saline   nature,    and   those   very  subtle, 
nimble,  and  of  very  great  fermentative  power,  are  separated 
from  the  air  by  the  aid  of  the  lungs  and  introduced  into  the 
mass  of  the  blood.     And  so  necessary  for  life  of  every  kind 
is  that  aereal  salt  (constituent)  that  not  even   plants  can 
grow  in  earth  the  access  of  air  to  which  is  shut  off.     But  if 
that  same  earth  be  exposed  to  air  and  so  forthwith  impreg- 
nated with  that  fecundating  salt,  it  at  once  becomes  fit  again 


56  THE  NUTRITION  OF  MAN 

for  growing."1  Mayow  fully  appreciated  the  importance  of 
his  nitro-aereal  particles  in  the  processes  of  life ;  he  had  in- 
deed a  fairly  accurate  conception  of  a  sound  theory  of  animal 
heat ;  he  saw  that  they  were  equally  necessary  for  burning, 
or  combustion,  and  for  respiration,  and  so  was  enabled  to 
draw  a  parallelism  between  the  two  processes;  he  pointed 
out  that  they  were  essential  for  the  ordinary  activity  of  the 
muscles  of  the  body,  that  as  muscle  work  was  increased  more 
particles  from  the  air  were  required ;  indeed,  he  clearly  fore- 
saw the  need  which  the  body  had  for  these  igneo-aereal  par- 
ticles in  all  the  chemical  processes  of  life.  And  thus  was 
foreshadowed  a  conception  of  oxidation,  a  hundred  years  be- 
fore Priestley  evolved  his  phlogiston  theories  and  Lavoisier 
discovered  oxygen. 

The  discoveries  of  Lavoisier,  published  in  1789,  led  to  a 
clear  understanding  of  combustion  as  a  process  of  oxidation, 
and  paved  the  way  for  a  fuller  knowledge  of  the  part  played 
by  the  oxygen  of  the  air  in  the  chemical  reactions  going  on  in 
the  animal  body.  Lavoisier  showed  that  the  oxygen  drawn 
into  the  lungs  with  the  air  breathed  was  used  in  the  body  for 
the  oxidation  of  certain  substances,  carbon  being  transformed 
thereby  into  carbon  dioxide,  and  hydrogen  into  water.  Fur- 
ther, he  noted  that  these  oxidations  were  carried  forward  on 
a  large  scale,  and  he  emphasized  the  importance  of  oxygen 
as  being  the  true  cause  of  the  varied  decompositions  taking 
place  in  the  living  body.  The  larger  the  amount  of  oxygen 
inspired,  the  more  extensive  the  oxidation,  and  consequently 
the  rate  of  respiration  as  modifying  the  intake  of  oxgyen 
served  in  his  opinion  as  a  regulator  to  control  the  extent  of 
the  oxidative  processes.  He  pointed  out  that  a  definite  rela- 
tionship existed  between  the  amount  of  work  done  by  the 
body  and  the  oxygen  consumed;  greater  muscular  activity, 
lower  temperature  of  the  surrounding  air,  the  activities  at- 

1  Quoted  from  Foster's  Lectures,  p.  195. 


ABSORPTION,    ASSIMILATION,   METABOLISM     57 

tending  the  digestive  functions,  all  seemed  to  be  associated 
with  a  greater  utilization  of  oxygen.  Oxidation  was  the 
pivot  around  which  all  the  chemical  reactions  of  the  body 
seemed  to  centre.  Lavoisier,  however,  was  not  a  physiologist, 
and  he  was,  quite  naturally  perhaps,  led  into  some  errors. 
For  example,  he  considered  that  the  process  of  combustion 
or  oxidation  took  place  in  the  lungs,  certain  fluids  rich  in 
carbon  and  hydrogen  formed  in  the  different  organs  of  the 
body  being  brought  there  for  exposure  to  the  inspired  oxy- 
gen. Further,  his  views  implied  a  simple  and  complete  com- 
bustion, in  which  complex  substances  rich  in  carbon  were 
directly  and  completely  oxidized  to  carbon  dioxide  and  water, 
in  much  the  same  manner  as  combustion  occurs  outside  the 
body.  Again,  he  assumed  that  the  amount  of  oxygen  taken 
into  the  lungs  determined  the  extent  of  oxidation,  just  as  the 
use  of  the  bellows,  by  increasing  the  draft  of  air,  causes  the 
fire  to  burn  more  brightly. 

To  Liebig  (1842)  the  next  great  advance  was  due.  This 
phenomenally  clear-minded  man,  while  recognizing  at  their 
full  value  the  fundamental  theories  advanced  by  Lavoisier, 
saw  and  fully  appreciated  their  incompleteness,  and  he  like- 
wise understood  their  failure  to  explain  many  of  the  phe- 
nomena of  life  more  familiar  to  the  physiological  mind  than 
to  that  of  a  simple  chemist  like  Lavoisier.  Liebig  had  made 
a  special  study  of  the  chemical  composition  of  foodstuffs,  and 
likewise  of  the  tissues  and  organs  of  the  body.  He  had, 
moreover,  given  great  attention  to  the  decomposition  products 
formed  in  the  body,  especially  the  nitrogenous  substances  ex- 
creted through  the  kidneys,  as  well  as  the  carbon  dioxide  and 
water  passed  out  through  the  lungs  and  skin.  It  was  not 
strange,  therefore,  that  he  should  take  exception  to  Lavoi- 
sier's view  that  oxidation  in  the  body  consisted  in  the  com- 
bustion of  a  fluid,  rich  in  carbon  and  hydrogen,  which  was 
brought  to  the  lungs.  On  the  contrary,  Liebig  contended 


58  THE  NUTRITION  OF  MAN 

that  it  was  the  organic  compounds,  proteids,  fats,  and  carbo- 
hydrates, that  underwent  oxidation,  and  not  necessarily  in 
the  lungs,  but  all  over  the  body,  wherever  organs  and  tissues 
were  active.  Especially  noteworthy  was  the  view  advanced 
by  Liebig,  and  upheld  for  many  years,  that  of  these  three 
classes  of  compounds  the  proteids  alone  served  for  the  con- 
struction of  organized  tissues,  like  muscle,  and  that  in  the 
activity  of  this  tissue,  as  in  muscle  contraction  or  musclt 
work,  the  energy  for  the  work  was  derived  solely  from  the 
breaking  down  or  oxidation  of  this  organized  proteid.  On 
this  ground  he  termed  the  proteid  foodstuffs  "plastic,"  or 
tissue-building  foods.  Liebig  further  pointed  out  that  the 
substances  of  the  body  have  the  power  of  combining  with  and 
holding  on  to  the  inspired  oxygen,  and  that  fats  and  carbo- 
hydrates, i.  £.,  the  non-nitrogenous  compounds,  easily  un- 
dergo oxidation  or  combustion,  and  thereby  furnish  the  heat 
of  .the  body.  For  this  reason  he  termed  the  corresponding 
foodstuffs  "  respiratory  "  foods.  Proteids,  on  the  other  hand, 
according  to  Liebig's  view,  are  capable  of  combustion  only 
in  slight  degree.  The  cause  of  the  decomposition  of  proteid 
substances  in  the  body  was  to  be  traced  solely  to  muscle 
work,  i.  e.,  the  energy  of  muscle  contraction,  or  muscle  work, 
was  derived  from  the  breaking  down  of  the  proteids  of  the 
muscle  tissue,  and  work  was  the  stimulus  which  brought 
about  proteid  decomposition.  Non-nitrogenous  substances 
played  no  part  in  these  reactions ;  muscle  work  was  without 
influence  on  these  compounds,  oxygen  being  the  sole  stimulus 
which  led  to  their  combustion,  and  heat  was  the  sole  product 
of  the  combustion. 

'  If  Liebig's  theory  is  correct,  that  the  proteids  of  the  body 
are  decomposed  only  as  the  result  or  the  accompaniment  of 
muscle  work,  and  the  proteids  of  the  food  are  used  up  only 
as  they  take  the  place  of  the  organized  proteid  so  metabolized, 
it  follows  that  with  a  like  degree  of  muscular  activity  a  given 


ABSORPTION,  ASSIMILATION,    METABOLISM      59 

body  will  always  decompose  the  same  amount  of  proteid.  If 
excess  of  proteid  food  is  taken,  the  surplus  will  be  stored  in 
the  tissues,  or,  in  other  words,  the  excretion  of  nitrogen  will 
not  be  influenced  by  the  amount  of  proteid  consumed  in  the 
food.  This  was  the  line  of  argument  made  use  of  by  various 
physiologists  l  who  were  disposed  to  criticise  Liebig's  view, 
and  quite  naturally  the  question  was  soon  made  the  subject 
of  many  experiments.  It  will  suffice  here  merely  to  say  that 
many  concordant  results  were  obtained,  showing  that  an 
abundance  of  proteid  food  leads  to  an  increase  in  the  excre- 
tion of  nitrogen,  muscle  activity  remaining  at  a  constant 
level.  Hence,  as  Voit  states,  some  other  ground  than  muscle 
work  must  be  sought  as  the  true  cause  of  proteid  katabolism. 
Consequently,  we  find  this  hypothesis  of  Liebig  replaced  by 
the  theory  of  "luxus  consumption,"  in  which' it  is  maintained 
that  while  whatever  proteid  is  used  up  by  the  work  of  the 
muscle  must  be  made  good  from  the  proteid  of  the  food,  any 
excess  of  proteid  absorbed  from  the  intestinal  canal  is  to  be 
considered  as  "luxus,"  and  like  the  non-nitrogenous  foods 
may  be  burned  up  in  the  blood,  by  the  oxygen  therein,  with- 
out being  previously  organized.  Hence,  we  see  suggested 
two  causes  for  the  decomposition  of  proteid  in  the  body,  viz., 
the  work  of  the  muscle  and  the  oxygen  of  the  blood.  Fur- 
ther, as  stated  by  C.  Voit,2  the  nitrogen  excretion  of  the 
hungry  or  fasting  animal  affords,  according  to  these  views, 
a  measure  of  the  extent  to  which  tissue  proteid  must  be 
broken  down  in  the  maintenance  of  life,  and  of  the  amount 
of  proteid  food  necessary  to  be  consumed  in  order  to  make 
good  the  loss;  viz.,  the  minimum  proteid  requirement. 
Again,  since  any  excess  of  proteid  food  beyond  this  minimal 
requirement,  according  to  the  theory,  is  destined  to  be  burned 


1  See   C.   Voit :    Hermann's    Handbuch    der    physiologie    des    Gesammt- 
Stoffwechsels.    Band  6,  Theil  1,  p.  269,  1881. 
a  Loc.  cit.,  p.  270. 


60  THE  NUTRITION  OF  MAN 

up  in  the  blood,  or  elsewhere,  to  furnish  heat  the  same  as  non- 
nitrogenous  foods,  it  follows  that  the  excess  of  proteid  food 
can  be  replaced  by  non-nitrogenous  aliment. 

Oxidation,  however,  is  the  keynote  in  any  explanation  of 
the  processes  of  metabolism,  whether  nitrogenous  or  non- 
nitrogenous  matter  is  involved.  Both  alike  undergo  oxida- 
tion, but  it  is  not  simple  oxidation  or  combustion  that  we 
have  to  deal  with.  In  the  time  of  Lavoisier,  as  already 
stated,  it  was  thought  that  oxygen  alone  was  the  cause  of 
the  decomposition  going  on  in  the  body,  but  simply  increas- 
ing the  intake  of  air  or  oxygen,  as  in  quickened  breathing 
or  deeper  inspiration,  does  not  increase  correspondingly  the 
rate  of  oxidation.  In  other  words,  it  is  not  a  direct  com- 
bination of  oxygen  with  the  carbon  and  hydrogen  of  the 
foodstuffs,  or  tissue  elements,  that  takes  place  in  the  body, 
but  rather  a  gradual,  progressive  decomposition  of  complex 
organic  compounds  into  simpler  products;  made  possible, 
however,  by  the  agency  of  the  oxygen  carried  from  the  lungs 
by  the  circulating  blood.  It  was  demonstrated  years  ago  that 
animals  breathing  pure  oxygen  do  not  consume  any  more  of 
the  gas  than  when  breathing  ordinary  air,  and  likewise  no 
more  carbon  dioxide  is  produced  in  the  one  case  than  in 
the  other.  Fifty  years  ago,  Liebig  and  other  physiologists 
showed  that  frogs'  muscle  placed  in  an  atmosphere  free  of 
oxygen  could  be  made  to  contract  or  do  work  for  some 
considerable  time,  and  with  liberation  of  heat.  This  fact 
implies  a  breaking  down  of  muscle  substance  into  simpler 
bodies,  but  there  is  here  no  free  oxygen  to  act  as  the  inciting 
cause ;  indeed,  what  actually  occurs  is  a  cleavage  or  splitting 
up  of  substances  in  the  muscle  tissue,  but  at  the  expense  of 
oxygen  in  some  form  of  combination  in  the  muscle.  This 
oxygen  must  have  been  taken  from  the  blood  at  some  pre- 
vious time  and  stored  in  the  tissue  for  future  use.  Again, 
as  C.  Voit  has  expressed  it,  if  oxygen  were  really  the  imme- 


ABSOKPT10N,    ASSIMILATION,   METABOLISM      61 

diate  cause  of  the  decompositions  taking  place  in  the  organ- 
ism, we  should  expect  combustion  to  occur  in  harmony  with 
the  well-known  relationship  of  the  three  classes  of  organic 
foodstuffs  to  oxygen.  In  other  words,  fats  would  undergo 
combustion  most  readily,  carbohydrates  next,  and  lastly  the 
nitrogenous  or  albuminous  compounds.  In  reality,  however, 
proteid  matter  is  decomposed  in  largest  quantity ;  a  generous 
addition  of  proteid  food  is  always  accompanied  by  an  in- 
creased consumption  of  oxygen.  Yet  oxygen  is  not  the 
inciting  cause  of  the  proteid  decomposition,  as  is  seen  from 
the  fact  that  in  muscle  work,  where  the  intake  of  oxygen  is 
greatly  increased,  there  is  no  noticeable  change  in  the  amount 
of  proteid  material  broken  down.  Plainly,  in  the  body  we 
have  to  deal  not  with  a  direct  oxidation  of  the  complex  com- 
pounds of  the  tissues  or  of  the  food,  but  rather  with  a  gradual 
cleavage  of  these  higher  compounds  into  simpler  substances, 
these  latter  undergoing  progressively  a  still  further  breaking 
down  with  intake  of  oxygen.  To  repeat,  oxygen  i§  not  the 
cause  of  the  decompositions  within  the  body,  but  the  extent  of 
the  breaking  down  of  the  tissue  or  food  material  is  the  deter- 
mining factor  in  the  amount  of  oxygen  taken  on  and  used  up. 
The  products  of  decomposition  contain  more  oxygen  than  the 
original  substances  undergoing  the  breaking  down  process, 
which  means  that  oxygen  is  taken  from  the  blood  and  used 
in  the  physiological  combustion  that  is  going  on.  It  is  not, 
however,  strictly  a  combustion  process;  it  is  more  compli- 
cated and  more  gradual  than  ordinary  combustion,  involving 
first  of  all  a  series  of  what  may  be  termed  oxidative  cleavages, 
in  which  large  molecules  are  gradually,  step  by  step,  broken 
down  into  simpler  molecules,  and  these  latter  then  oxidized 
to  still  simpler  forms.  Hence,  we  find  the  oxidative  changes 
preceded  by  a  variety  of  alterations  in  which  oxygen  may 
take  no  part  whatever;  such  as  hydrolytic  cleavage,  where 
the  elements  of  water  are  taken  on  as  a  necessary  step  in  the 


62  THE  NUTBITION  OF  MAN 

cleavage  process;  dissociation  of  a  simple  sort,  as  when  a 
large  molecule  breaks  up  directly  into  smaller  molecules,  etc. 
These  statements  by  no  means  detract  from  the  importance 
of  oxygen  in  the  katabolic  processes  of  the  body,  but  it  is 
physiological  oxidation  that  we  have  to  do  with,  and  not 
simple  combustion.  Oxygen  is  not  the  direct  cause  of  the 
transformations  taking  place  in  the  body.  As  one  looks 
over  the  history  of  progress  in  our  knowledge  of  nutrition 
from  the  time  of  Lavoisier  to  the  present,  it  is  easy  to  note 
the  gradual  change  of  view  regarding  oxidation  in  the  living 
organism.  Step  by  step,  it  has  been  demonstrated  that  there 
are  many  factors  involved  in  this  breaking  down  of  complex 
substances;  that  while  oxygen  is  an  ever  present  require- 
ment, there  are  other  equally  important  factors  to  be  taken 
into  account.  The  contrast  between  the  older  views  and 
those  now  current  is  clearly  shown  by  the  difference  in  atti- 
tude regarding  the  place  in  the  body  where  oxidation  occurs. 
Thus,  in  the  earlier  days,  when  the  view  was  gradually  gain- 
ing ground  that  nutritional  changes  were  mainly  the  result 
of  oxidation,  and  that  the  oxygen  drawn  into  the  lungs  in 
inspiration  was  a  primary  factor,  then,  as  we  have  seen,  the 
lungs  were  considered  as  the  laboratory  where  the  transforma- 
tion takes  place.  This  view,  however,  was  soon  exploded, 
and  next  we  find  the  blood,  the  lymph,  and  other  fluids,  but 
especially  the  blood,  looked  on  as  the  locality  where  oxidation 
occurs.  This  was  indeed  quite  a  natural  view  to  hold,  since 
the  blood  is  the  carrier  of  oxygen,  but  we  now  know,  in  har- 
mony with  the  fact  that  the  breaking  down  of  complex  food 
material  is  a  complicated  process,  involving  various  kinds  of 
chemical  change,  that  these  katabolic  processes  are  not  located 
in  any  one  place,  but  occur  all  over  the  body  wherever  there 
are  active  tissues.  As  has  been  previously  stated,  the  human 
body  is  a  "  nation  "  of  cells,  all  of  which  are  more  or  less 
active,  and  it  is  in  these  miniature  laboratories  mainly  that 


ABSORPTION,   ASSIMILATION,  METABOLISM      63 

oxidation  and  all  the  other  nutritional  changes  coincident  to 
life  take  place.  Muscle  tissue  and  nerve  tissue,  the  large 
secreting  glands,  such  as  the  liver,  stomach,  and  pancreas, 
all  are  the  seat  of  oxidative  and  other  changes  which  we 
class  under  the  broad  term  of  nutritional.  To  these  cells, 
therefore,  we  must  look  for  an  explanation  of  the  causes  of 
oxidation,  and  the  other  transformations  of  a  kindred  nature 
that  take  place  in  the  body. 

In  our  brief  survey  of  digestion,  and  of  the  methods  there 
followed  for  the  proper  utilization  of  the  organic  foodstuffs, 
it  was  seen  that  the  unorganized  ferments  or  enzymes  are  the 
active  agents  in  accomplishing  the  breaking  down  of  proteids, 
and  the  less  profound  alteration  of  fats  and  carbohydrates. 
Is  it  not  possible  that  the  tissues  of  the  body  are  like.wise 
supplied  with  enzymes  of  various  types,  and  that  upon  these 
powerful  agents  rests  the  responsibility  for  the  different 
kinds  of  decomposition,  oxidation  and  other  changes,  that 
take  place  in  the  body  ?  Some  years  ago  much  interest  was 
aroused  by  the  observation  that  certain  glands  in  the  body, 
if  simply  warmed  at  body  temperature  with  water,  in  the 
presence  of  some  germicidal  agent  sufficient  to  prevent  putre- 
factive changes,  underwent  what  is  now  termed  autodigestion, 
i.  e.,  a  process  of  self-digestion,  with  formation  of  various 
products,  notably  such  as  would  naturally  result  from  the 
breaking  down  of  proteid  material  by  ordinary  proteolytic 
enzymes.  This  would  seem  to  imply  the  presence  in  the 
glands  of  a  proteid-splitting  enzyme,  the  products  formed 
being  proteoses,  peptones,  amino-acids,  etc.,  just  such  products 
as  result  from  the  action  of  trypsin.  To-day,  we  know  that 
practically  all  tissues  and  organs  can,  under  suitable  condi- 
tions, undergo  autolysis,  and  in  many  instances  the  enzymes 
themselves  can  be  separated  from  the  tissues  by  appropriate 
treatment.  Liver,  muscle,  lymph  glands,  spleen,  kidneys, 
lungs,  thymus,  etc.,  all  contain  what  are  very  appropriately 


64  THE  NUTRITION   OF  MAN 

called  intracellular  enzymes.  These  enzymes  are  of  various 
kinds.  Especially  conspicuous  are  the  hydrolytic,  proteid- 
splitting  enzymes,  which  behave  in  a  manner  quite  similar 
to,  if  not  identical  with,  that  of  the  digestive  enzymes  of 
the  gastro-intestinal  tract,  i.  e.,  pepsin,  trypsin,  and  erepsin. 
Further,  there  are  other  hydrolytic  cleavages  taking  place  in 
tissue  cells,  such  as  the  cleavage  of  fats,  due  as  we  now  know 
to  intracellular  enzymes  of  the  lipase  type,  and  by  which 
neutral  fats  are  split  apart  into  glycerin  and  fatty  acid. 
Again,  there  are  in  many  organs  intracellular  enzymes  which 
act  upon  the  complex  nucleoproteids  of  the  tissue,  causing 
them  to  break  apart  into  proteid  and  nucleic  acid,  the  latter 
being  further  broken  down  by  other  enzymes  with  liberation 
of  the  contained  nuclein  or  purin  bases.  Many  other  chem- 
ical reactions  are  brought  about  by  specific  enzymes  of  various 
kinds,  present  in  the  cells  of  particular  glandular  organs. 
Thus,  intracellular  enzymes  have  been  found,  as  in  the  liver, 
which  are  able  to  transform  amino-acids  into  amides,  and  still 
others  capable  of  splitting  up  amides. 

Equally  important,  and  even  more  suggestive,  are  the  data 
which  have  been  collected  recently  regarding  oxidative  proc- 
esses in  the  tissues  of  the  body.  Specific  ferments,  known 
as  oxidases,  are  found  widely  distributed  in  many  organs  and 
tissues,  and  it  is  difficult  to  escape  the  conclusion  that  as  in- 
tracellular enzymes  they  have  an  important  part  to  play  in 
some,  at  least,  of  the  transformations  characteristic  of  tissue 
katabolism.1  As  a  single  example,  mention  may  be  made  of 
aldehydase,  which  accomplishes  the  oxidation  of  substances 
having  the  structure  of  aldehydes  into  corresponding  acids. 
Ferments  or  enzymes  of  this  class  are  found  in  the  liver, 


1  See  M.  Jacoby :  Ueber  die  Bedeutung  der  intracellularen  Ferraente  fur  die 
Physiologic  und  Patbologie.  Ergebnisse  der  Physiologic,  Erster  Jahrgang, 
1.  Abtheilung,  p.  230 


ABSOBPTION,  ASSIMILATION,    METABOLISM     65 

spleen,  salivary  glands,  lungs,  brain,  kidneys,  etc.,  and  they 
may  well  be  considered  as  important  agents  in  the  chemical 
transformations  going  on  in  the  tissues  of  the  body.  It  would 
take  us  too  far  afield  to  enter  into  a  detailed  consideration  of 
these  intracellular  enzymes ;  it  must  suffice  to  emphasize  the 
general  fact  that  in  all  the  tissues  and  organs  of  the  body  there 
are  present  a  large  number  of  enzymes  of  different  types,  en- 
dowed with  different  lines  of  activity,  and  consequently  capa- 
ble of  accomplishing  a  great  variety  of  results  in  metabolism. 
Oxidation  may  still  be  a  dominant  feature  in  nutrition,  oxida- 
tive  changes  may  characterize  more  or  less  every  tissue  and 
organ  in  the  body,  but  the  processes  are  subtle  and  are  not  to 
be  denned  in  harmony  with  simple  chemical  or  physical  laws. 
The  living  cell,  with  its  intracellular  enzymes,  is  the  guiding 
and  controlling  power  by  which  the  processes  of  katabolism  are 
regulated  in  harmony  with  the  needs  of  the  body.  Complex 
organic  matter  is  broken  down  step  by  step  in  the  various 
tissues,  with  gradual  liberation  of  the  contained  energy; 
processes  of  hydrolytic  cleavage  alternate  with  processes  of 
oxidation,  the  molecules  acted  upon  growing  smaller  with 
each  downward  step,  until  at  last  the  final  end-products  are 
reached,  viz.,  carbon  dioxide,  water,  and  urea,  which  the 
body  eliminates  through  various  channels  as  true  physio- 
logical waste-products. 

It  will  be  advisable  for  us  to  consider  briefly  some  of  these 
intermediary  products  of  tissue  metabolism,  since  in  any  dis- 
cussion of  nutritive  changes  it  is  quite  essential  to  have  some 
understanding  of  the  chemical  relationship  existing  between 
the  various  products  which  result  from  the  breaking  down 
of  .proteid  and  other  materials  in  tissue  katabolism.  This  is 
especially  true  of  proteid  material,  since  in  the  gradual  dis- 
integration of  this  substance  in  tissue  metabolism  many  in- 
termediary bodies  are  formed,  which  undoubtedly  exercise 
some  physiological  influence  prior  to  their  transformation 


66  THE  NUTRITION   OF   MAN 

into  simpler  bodies,  with  ultimate  fornication  of  the  final 
product,  urea.  As  has  been  pointed  out  so  many  times,  the 
proteid  foods  are  peculiar  in  that  they  alone  contain  the  nec- 
essary nitrogen,  and  in  the  peculiar  form  able  to  meet  the 
physiological  requirements  of  the  body.  Variations  in  the 
proteid  intake  are  of  necessity  accompanied  by  variations  in 
the  formation  of  nitrogenous  intermediary  products,  and  both 
quality  and  quantity  of  these  substances  must  be  given  due 
attention  in  any  study  of  nutrition.  Further,  it  is  only  by 
an  understanding  of  the  general  or  ground  structure  of  pro- 
teids  that  we  can  hope  to  attain  knowledge  of  the  processes 
going  on  in  the  different  tissues  and  organs  in  connection 
with  metabolism,  while  a  true  appreciation  of  the  chemical 
peculiarities  of  the  individual  proteids  will  help  to  explain  the 
different  nutritional  value  of  vegetable  as  contrasted  with 
animal  proteids. 

Our  understanding  of  the  chemical  structure  of  any  or- 
ganic substance  is  based  primarily  upon  a  study  of  the  de- 
composition products  which  result  from  its  breaking  down, 
under  'the  influence  of  various  chemical  agencies.  Simple 
proteid  substances  when  acted  upon  by  pancreatic  juice  re- 
inforced by  the  enzyme  erepsin,  or  when  boiled  with  dilute 
acids,  undergo  hydrolytic  cleavage  with  ultimate  formation  of 
a  large  number  of  relatively  simple  bodies,  mostly  amino- 
acids,  the  chemical  structure  of  which  throws  some  light 
upon  the  nature  of  the  proteid.  Thus,  in  the  pancreatic 
digestion  of  proteid  in  the  intestine  we  may  adopt  the  fol- 
lowing scheme  as  showing  in  a  general  way  the  progressive 
transformation  that  occurs,  understanding  at  the  same  time 
that  like  transformations  may  be  accomplished  by  corre- 
sponding intracellular  enzymes  in  the  tissues  and  organs  of 
the  body ;  and  further,  that  by  the  long-continued  action  of 
hydrolytic  agents  there  is  a  complete  breaking  down  into 
amino-acids  and  other  simple  products. 


ABSORPTION,    ASSIMILATION,   METABOLISM     6T 

Native  Proteid 


Protoproteose  Heteroproteose  :  Primary  proteoses 

Deuteroproteose  Deuteroproteose  :  Secondary  proteoses 

Peptone  Peptone 

Amino-acids  Amino-acids 


Among  these  end-products,  or  ammo-acids,  are  leucin, 
tyrosin,  aspartic  acid,  glutaminic  acid,  glycocoll,  arginin, 
lysin,  histidin,  and  likewise  the  peculiar  aromatic  body  tryp- 
tophan.  The  chemical  make-up  of  these  substances  may  be 
indicated  by  the  following  structural  formulae,  which,  if  even 
only  partially  understood,  will  suggest  to  the  non-chemical 
mind  some  idea  of  close  chemical  relationship: 


.     CH  (NH2)  COOH  CH  (NH2)  COOH 

CH2^  I 

\CH2-COOH  CH2-COOH 

Glutaminic  acid  Aspartic  acid 


jfLa   1>  -Clo  JJXlo  . 

L  _3>CH-CH2-CH(NH2)-COOH 


CH2  -  NH2  CH 

COOH  CH8  ^ 

Glycocoll  Leucin 


/OH 
XCH2-CH(NH2)COOH 

Tyrosin  C  •  CH2  •  CH  •  (NH2)  •  COOH 

/  ^ 

[4      CH 
\  / 
NH 

Tryptophan 


68  THE  NUTRITION   OF   MAN 


CH2-NHV  CH2-NH2 

|  \C  -  NH2       I 

CH2      NH^  CH2 

CH2  CH2  GH2 

CH    •   NH,  CH2  CH-NH, 

COOH  CH  -  NH,  COOH 

COOH 

Arginin  Histidin 

Lysin 


In  these  various  decomposition  products  there  is  apparent 
certain  definite  lines  of  resemblance,  on  which  is  based  one 
or  more  suggestions  regarding  possible  ways  in  which  these 
chemical  groups  are  linked,  or  bound  together,  in  the  proteid 
molecule.  Thus,  there  is  apparently  present  a  complex  or 
nucleus  which  may  be  indicated  as 

HC  -  NH  -  CO  -         also        HO  -  NH  -  C  (NH)  - 


The  proteid  molecule  is  presumably  built  up  of  amino- 
acids  variously  joined  together,  this  synthesis  being  accom- 
plished, doubtless,  by  the  condensation  of  different  types  of 
amino-acids,  in  which  the  first  of  the  above  groups  represents 
the  more  common  method  of  union.  We  may  indeed  conjec- 
ture that  such  methods  of  condensation  take  place  in  the 
human  body,  in  the  epithelial  cells  of  the  intestine,  and  in  the 
tissues  in  general ;  and  that  by  such  methods,  construction  of 
proteid  is  accomplished  out  of  the  various  fragments  split  off 
by  digestion,  etc.  In  a  tentative  way,  the  principle  may  be 
illustrated  by  the  fusion  of  leucin  and  glutaminic  acid,  — fol- 
lowing Hofmeister's  suggestion,  —  in  which  a  still  larger 
complex  is  formed: 


ABSORPTION,   ASSIMILATION,   METABOLISM      69 

-CO  4  NH-CH-CO-NH-CH-CO-L  NH — 

i  I  I  i 

C4H,  (CH2)2 

ci-OH 

Leucin  Glutarainic  acid 

In  this  way,  step  by  step,  the  proteid  molecule  is  built  up, 
and  naturally  in  katabolism  the  proteid  breaks  down  along 
certain  definite  lines  of  cleavage,  with  formation  of  katabolic 
products  containing  those  groups,  or  chemical  nuclei,  which 
characterize  the  different  proteid  molecules.  For  it  is  to  be 
clearly  understood  that  there  are  many  different  forms  of 
proteid,  perhaps  superficially  alike,  but  possessed  of  physio- 
logical individuality.  This  is  well  illustrated  by  the  two 
primary  proteoses  formed  in  digestion.  As  will  be  recalled, 
there  are  at  first  two  proteoses  produced,  protoproteose  and 
heteroproteose.  These  are,  superficially  at  least,  not  radi- 
cally unlike;  they  possess  essentially  the  same  percentage 
composition,  but  when  broken  down  by  vigorous  chemical 
methods  they  show  a  totally  different  make-up.  In  other 
words,  at  the  very  beginning  of  digestion  there  is  a  splitting 
up  of  the  proteid  into  two  parts,  which  have  quite  a  different 
chemical  structure,  as  is  clearly  indicated  by  the  difference  in 
the  character  and  amount  of  the  decomposition  products 
yielded  by  hydrolytic  cleavage.  Thus,  heteroalbumose  as 
derived  from  blood-fibrin  contains  39  per  cent  of  its  total 
nitrogen  in  basic  form,  i.  e.,  in  a  form  which  goes  over  into 
the  basic  bodies,  arginin,  lysin,  and  histidin,  etc.  On  the 
other  hand,  protoalbumose  from  the  same  source  yields  hardly 
25  per  cent  of  basic  nitrogen.  Further,  heteroalbumose  yields 
only  a  very  small  amount  of  tyrosin,  while  protoalbumose 
gives  on  decomposition  a  large  amount  of  this  substance. 
Again,  heteroalbumose  furnishes  a  large  yield  of  leucin 
and  glycocoll,  while  protoalbumose  gives  no  glycocoll  and 


70 


THE  NUTRITION   OF  MAN 


only  a  little  leucin.  Obviously,  these  two  proteoses  have 
an  inner  structure  quite  divergent  one  from  the  other,  and 
owing  to  this  fact  they  must  play  a  quite  different  role  in 
metabolism. 

Even  greater  differences  in  inner  chemical  structure  are 
found  among  native  proteids.  By  way  of  illustration,  we 
may  take  egg-albumin,  the  casein  of  cow's  milk,  gliadin  of 
wheat,  and  the  edestin  of  hemp  seed.  These  are  all  typical 
proteids ;  they  are  all  useful  as  food,  but  they  are  radically 
different  in  their  inner  chemical  structure,  as  is  clearly  in- 
dicated by  the  following  data,1  which'  show  the  percentage 
yield  of  the  different  amino-acids  and  ammonia: 


Leucin. 

Tyrosin. 

Gluta- 
minic  Acid. 

Arginin. 

Lysin. 

Histidin. 

Ammonia. 

Egg-albumin  . 

6.1 

1.1 

9.0 

.  .  . 

.  .  . 

.  .  . 

1.6 

Casein    .    .    . 

10.6 

4.5 

10.7 

4.8 

5.8 

2.6 

1.9 

Gliadin  .    .    . 

5.7 

1.2 

37.3 

3.2 

0 

0.6 

5.1 

Edestin  .    .    . 

19.9 

2.7 

14.0 

14.2 

1.6 

2.2 

2.3 

These  are  not  mere  technical  differences,  but  they  repre- 
sent divergences  of  structure  which  cannot  help  counting  as 
material  factors  in  nutritional  processes.  Especially  notice- 
able is  the  large  yield  of  glutaminic  acid  from  wheat  proteid, 
as  contrasted  with  the  proteid  (casein)  of  animal  origin.  As  a 
rule,  glutaminic  acid  forms  a  larger  proportion  of  the  decom- 
position products  of  vegetable  than  of  animal  proteids.  Simi- 
larly, arginin  is  present  in  much  larger  proportion  in  most 
vegetable  proteids  than  in  most  animal  proteids.  While 
many  other  data  more  or  less  trustworthy  might  be  added, 
these  figures  will  suffice  to  emphasize  the  main  point  under 
discussion,  viz.,  that  individual  proteids  show  marked  varia- 


1  These  data  were  furnished  the  writer  by   Dr.  Thomas  B.  Osborne,  and 
represent  in  large  measure  the  results  of  his  own  chemical  work. 


ABSOBPTION,   ASSIMILATION,    METABOLISM      71 

tion  in  the  amount  of  the  several  ammo-acids  which  serve  as 
corner-stones  or  nuclei  in  the  building  up  of  the  molecule, 
and  consequently  they  must  yield  correspondingly  different 
katabolic  products  when  serving  the  body  as  food. 

Turning  now  to  another  phase  of  tissue  metabolism,  we 
may  consider  briefly  the  nucleoproteids  and  their  character- 
istic decomposition  products;  bodies  which  are  widely  dis- 
tributed as  cleavage  products  formed  in  the  disintegration  of 
most  cell  protoplasm,  and  having  special  interest  in  nutri- 
tion because  of  their  chemical  relationship  to  that  well-known 
substance,  uric  acid.  Nucleoproteids  of  some  type  are  found 
in  all  cells ;  consequently  they  are  present  in  all  tissues,  in 
all  glandular  organs,  and  their  widespread  distribution  con- 
stitutes evidence  of  their  great  physiological  importance. 
Nucleoproteids  are  compound  substances  made  up  of  some 
form  of  proteid  and  nucleic  acid.  By  simple  hydrolysis  with 
dilute  mineral  acids  they  are  broken  down  into  proteid, 
phosphoric  acid,  and  one  or  more  bodies  known  as  nuclein 
bases.  Of  these  latter  substances,  there  are  four  well-defined 
bodies,  viz.,  adenin,  hypoxanthin,  guanin,  and  xanthin,  which 
from  their  peculiar  chemical  constitution  are  known  as  "  purin 
bases."  In  the  body,  there  is  present  in  many  cells  a  peculiar 
intracellular  enzyme  termed  nuclease,  which  has  the  power 
of  liberating  these  purin  bases  from  their  combination  as  a 
component  part  of  tissue  nucleoproteids,  or  of  the  contained 
nucleic  acid.  In  autolysis  or  self-digestion  of  many  glands, 
such  as  the  spleen,  thymus,  etc.,  this  chemical  reaction  is 
easily  induced  by  action  of  the  contained  nuclease.  Further, 
the  liberated  purin  bases  then  undergo  change  because  of 
the  presence  of  certain  deamidizing  enzymes,  and  as  a  result 
guanin  is  transformed  into  xanthin,  and  adenin  is  converted 
into  hypoxanthin.  These  ferments  are  true  intracellular 
enzymes,  and  are  termed  respectively  guanase  and  adenase. 
The  real  essence  of  the  reaction  they  accomplish  is  clearly  in- 


72  THE  NUTKITION  OF  MAN 

dicated  by  the  following  formulae,  which  likewise  show  the 
chemical  nature  and  relationship  of  the  four  substances  : 

HN  -  CO  HN  -  CO 

H2N-C       C-NHv          +H20=      CO     C-NHv  +  NH. 


Guanin  Xauthin 


N  =  C  •  NHa  HK  -  CO 

HC       C-NHV          +H20=     HC      C-NHV  +  NH. 


Adenin  Hypoxanthin 

These  two  enzymes  are  typical  hydrolyzing  enzymes,  but 
it  is  to  be  noted  that  there  is  not  only  a  taking  on  of  water 
with  a  retention  of  the  oxygen,  but  there  is  also  a  giving  off 
of  ammonia,  by  which  the  transformation  is  made  possible. 
Adenin  is  known  as  an  anrino-purin  and  guanin  as  an  amino- 
oxypurin,  while  hypoxanthin  is  an  oxypurin  and  xanthin  a 
dioxypurin.  In  other  words,  the  two  intracellular  enzymes 
are  able  to  transform  the  two  amino-purins  into  the  corre- 
sponding oxypurins;  i.  e.,  the  enzymes  are  deamidizing  fer- 
ments, liberating  the  NH2  group  of  the  adenin  and  guanin 
and  thus  forming  two  new  compounds.  These  reactions, 
though  more  or  less  technical,  are  emphasized  in  this  way  not 
merely  because  they  illustrate  the  action  of  intracellular 
enzymes  in  intermediary  metabolism,  thus  affording  a  striking 
example  of  the  gradual  changes  that  take  place  in  ordinary 
katabolic  processes,  but  especially  because  they  throw  light 
upon  the  production  of  another  substance  common  in  body 
metabolism,  viz.,  uric  acid.  It  has  long  been  known  that 
nucleoproteids,  nucleins,  and  other  compounds  containing 


ABSORPTION,   ASSIMILATION,  METABOLISM      73 

these  purin  radicles,  when  taken  as  food,  cause  at  once  an 
increased  output  of  uric  acid,  and  it  has  been  clearly  recog- 
nized that  in  some  way  this  latter  substance,  as  a  product  of 
metabolism,  must  come  from  the  transformation  of  nuclein 
bases.  To-day,  we  understand  that  in  many  tissues,  as  in  the 
liver,  spleen,  lungs,  and  muscle,  there  is  present  a  peculiar 
oxidizing  ferment,  an  oxidase,  by  the  action  of  which  hypo- 
xanthin  can  be  converted  into  xanthin,  and  the  latter  directly 
oxidized  to  uric  acid.  This  conversion  into  uric  acid  is  purely 
a  process  of  oxidation,  brought  about  by  a  typical  intracellular 
oxidase,  known  specifically  as  "xanthin  oxidase,"  the  reaction 
involved  being  as  follows  : 

HN  -  CO  HN  -  CO 

CO  C-NHV  +0=  CO    C-NH 

I       II  >CH  I        II  >CO 

HN  -  C  -  N  #  HIST  -  C  -  NH 

Xanthin  Uric  acid 

From  these  several  reactions,  it  is  clear  how  various  in- 
tracellulai'  enzymes  working  one  after  the  other  are  able 
gradually  to  evolve  uric  acid  from  tissue  nucleoproteids. 
Further,  it  is  to  be  noted  that  there  is  another  tissue  oxidase 
—  contained  principally  in  the  kidneys,  muscle,  and  liver  — 
which  has  the  power  of  oxidizing  and  thus  destroying  uric 
acid,  with  formation,  among  other  substances,  of  urea.  Re- 
membering that  urea  has  the  following  chemical  constitution 


it  is  easy  to  see,  by  comparison  of  the  formulae,  how  uric  acid 
might  easily  yield  two  molecules  of  urea  through  simple 
oxidation.  In  this  way,  excess  of  uric  acid  produced  in  the 


74  THE  NUTRITION  OF  MAN 

body  can  be  converted  into  urea,  and  in  this  harmless  form 
be  excreted  from  the  system. 

Finally,  reference  should  be  made  here  to  several  other 
products  of  tissue  metabolism,  products  of  the  breaking  down 
of  proteid  matter  in  the  body,  since  they  are  liable  to  prove  of 
interest  to  us  in  other  connections.  Thus  creatin,  abundant  in 
the  muscle  and  other  places  ;  the  related  substance  creatinin, 
present  in  the  urine  ;  methyl  guanidin,  a  decomposition  prod- 
uct of  creatin;  and  urea,  all  call  for  a  word  of  description. 
The  chemical  relationship  of  these  bodies  is  clearly  indicated 
by  the  following  formulae  : 

/NH2 
C=NH 
\N  (CH8)  CH2COOH  \N  (CH,)  CH2 

Creatin  Creatinin 

/NH2  /NH2 

C=NH  C=0 

\NH(CH3)  \NH2 

Methyl  guanidin  Urea 

Creatinin  is  chemically  the  anhydride  of  creatin,  i.  e.,  it  can 
be  formed  from  creatin  by  the  simple  extraction  of  one  mole- 
cule of  water,  H2O.  Creatin,  by  hydrolytic  cleavage,  will 
break  down  into  one  molecule  of  urea  and  one  molecule  of 
sarcosin  or  methyl  glycocoll,  as  shown  in  the  following 
equation  : 

CH2-NH-(CH8) 


\  N  (CH3)CH2COOH 

Creatin  Sarcosin  Urea 

Methyl  guanidin  is  a  decomposition  product  of  creatin,  while 
guanidin,  as  can  be  seen  from  the  formula,  is  like  urea,  ex- 


ABSORPTION,   ASSIMILATION,   METABOLISM      75 

cepting  that  the  group  NH  replaces  the  oxygen  of  urea. 
These  simple  statements  will  suffice  for  our  present  purpose, 
viz.,  to  indicate  the  more  or  less  close  chemical  relationships 
existing  between  many  of  these  nitrogenous  decomposition 
products  resulting  from  proteid  katabolism ;  also  to  suggest 
how  by  slight  chemical  alteration  one  decomposition  product 
may  be  resolved  into  another  related  substance  in  the  proc- 
esses of  katabolism.  Our  conception  of  the  processes  in- 
volved in  proteid  katabolism  is  that  of  a  series  of  progressive 
chemical  decompositions,  in  which  intracellular  enzymes  play 
the  all-important  part.  -The  intermediary  products  formed 
are  definite  bodies  because  of  the  specific  nature  of  the  active 
enzymes,  and,  secondly,  because  of  the  chemical  nature  of 
the  substances  acted  upon.  In  other  words,  oxidation  in 
the  animal  body  takes  the  shape  of  a  series  of  well-defined 
chemical  reactions,  in  which  chemical  constitution  and  specific 
enzyme  action  are  the  predetermining  cause.  In  the  absence 
of  the  particular  chemical  groups,  the  oxidase  is  unable  to 
bring  about  oxidation,  or,  given  the  proper  compound  or 
mother  substance  in  the  absence  of  the  specific  oxidase,  there 
is  no  oxidation.  Hence,  oxidation  in  the  animal  body  is  not 
the  result  of  simple  combustion,  but,  on  the  contrary,  it  con- 
sists of  a  series  of  orderly  chemical  processes,  each  one  of 
which  is  presided  over  by  an  intracellular  enyzme,  specific  in 
its  nature,  in  that  it  is  capable  of  acting  only  upon  substances 
having  a  certain  definite  constitution,  and  leading  invariably 
to  a  certain  definite  result.  The  processes  which  years  ago 
were  considered  as  due  to  the  peculiar  vital  properties  of  the 
tissue  cells,  and  which  were  supposed  to  be  entirely  de- 
pendent upon  their  morphological  and  functional  integrity, 
are  now  seen  to  be  due  primarily  to  a  great  variety  of 
enzymes,  manufactured  indeed  by  the  living  cells,  but  capa- 
ble of  manifesting  their  activity  even  when  free  from  the 
influence  of  the  living  protoplasm.  The  varied  processes  of 


76  THE  NUTRITION  OF  MAN 

tissue  katabolism  are  the  result  of  orderly  and  progressive 
chemical  changes,  in  which  cleavage,  hydrolysis,  reduction, 
oxidation,  deamidization,  etc.,  alternate  with  each  other 
under  the  influence  of  specific  enzymes,  where  chemical  con- 
stitution and  the  structural  make-up  of  the  various  molecules 
are  determining  factors  in  the  changes  produced. 


CHAPTER  III 
THE  BALANCE  OF  NUTRITION 

TOPICS:  Body  equilibrium.  Nitrogen  equilibrium.  Carbon  equilib- 
rium. Loss  of  nitrogen  during  fasting.  Influence  of  previous  diet 
on  loss  of  nitrogen  in  fasting.  Output  of  carbon  during  fasting. 
Influence  of  pure  proteid  diet  on  output  of  nitrogen.  Influence  of  fat 
on  proteid  metabolism.  Effect  of  carbohydrate  on  nitrogen  metabo- 
lism. Storing  up  of  proteid  by  the  body.  Transformation  of  energy 
in  the  body.  Respiration  calorimeter.  Basal  energy  exchange  of  the 
body.  Circumstances  influencing  energy  exchange.  Effect  of  food 
on  heat  production.  Respiratory  quotient  and  its  significance.  In- 
fluence of  muscle  work  on  energy  exchange.  Elimination  of  carbon 
dioxide  during  work  and  with  different  diets.  Effect  of  excessive 
muscular  work  on  energy  exchange.  Oxygen  consumption  under 
different  conditions.  Output  of  matter  and  energy  subject  to  great 
variation.  Body  equilibrium  and  approximate  nitrogen  balance  to  be 
expected  in  health. 

MAN,  strictly  speaking,  is  always  in  a  condition  of 
unequilibrium.  If  placed  upon  a  large  and  sensi- 
tive pair  of  scales  with  the  opposite  side  exactly  counter- 
poised, he  will  be  found  to  lose  weight  constantly  until  water 
or  food  are  taken,  when  the  losses  of  an  hour  or  two  may  be 
made  good,  or  perchance  more  than  balanced.  The  human 
body  is  a  maelstrom  of  chemical  changes ;  chemical  decompo- 
sitions are  taking  place  continuously  at  the  expense  of  the 
proteids,  fats,  and  carbohydrates  of  the  tissues  and  of  the 
food,  the  stored-up  energy  of  these  organic  compounds  being 
thereby  transformed  into  the  active  or  "kinetic"  forms  of 


78  THE  NUTKITION  OF  MAN 

heat  and  motion;  while  carbon  dioxide,  water,  urea,  and 
some  few  other  nitrogenous  substances  are  being  continually 
formed  as  the  normal  waste  products  of  these  tissue  changes, 
and  constantly  or  intermittently  excreted.  In  other  words, 
the  body  is  in  a  perpetual  condition  of  chemical  oscillation, 
constantly  consuming  its  own  substance,  rejecting  the  waste 
products  which  result,  and  giving  off  energy  in  the  several 
forms  characteristic  of  living  beings.  The  condition  of  the 
body  plainly  depends  upon  the  relation  which  it  is  able  to 
maintain  between  the  income  and  the  expenditure  of  matter 
and  energy.  If  the  income  equals  the  output,  the  body  is 
kept  in  a  condition  approaching  equilibrium;  if  the  intake 
exceeds  the  outgo,  the  body  adds  to  its  capital  of  matter  and 
energy ;  while  if  the  expenditure  is  greater  than  the  income, 
the  accumulated  capital  is  drawn  upon ;  and  this,  if  continued 
indefinitely,  results  in  a  drain  upon  the  bank  which  must 
eventually  end  in  disaster.  It  is  comparatively  easy,  how- 
ever, for  man  to  maintain  his  body  in  a  condition  of  equi- 
librium from  day  to  day;  i.  e.,  the  losses  of  the  morning  can 
be  made  good  at  luncheon,  or  the  expenditures  of  an  entire 
day  counterbalanced  by  a  corresponding  addition  to  capital 
the  following  day,  in  which  case  the  body  may  be  said  to  be 
in  balance.  It  is  necessary,  however,  to  discriminate  between 
body  equilibrium,  meaning  thereby  the  maintenance  from  day 
to  day  of  a  constant  body-weight,  and  nitrogen  equilibrium, 
or  carbon  equilibrium.  In  the  latter  cases,  what  is  meant  is 
that  the  intake  of  nitrogen,  or  of  carbon,  exactly  equals  the 
output  of  these  two  elements.  It  is  quite  possible,  however, 
to  have  a  condition  of  nitrogen  equilibrium  without  the  body 
being  in  a  state  of  balance,  as  when  the  outgo  of  carbon 
exceeds  the  intake  of  carbon,  or  when  there  is  an  increased 
output  of  water. 

As  a  rule,  it  may  be  stated  that  when  a  man  puts  out  less 
carbon  and  less  nitrogen  than  he  takes  in  he  must  be  gaining 


THE  BALANCE  OF  NUTRITION  79 

in  weight;  the  only  exception  being  the  possible  case  of  an 
increased  excretion  of  water,  which  might  more  than  counter- 
balance the  gain.  On  the  other  hand,  if  he  gives  off  more 
carbon  and  more  nitrogen  than  he  takes  in,  .the  body  must 
lose  in  weight.  Where  the  output  of  carbon  is  beyond  the 
amount  of  carbon  ingested,  the  lost  carbon  represents  a  drain 
upon  body  fat.  In  a  reversal  of  this  condition,  i.  e.,  where 
the  carbon  taken  in  is  in  excess  of  the  outgo,  the  body  is 
gaining  in  fat.  Theoretically,  gain  or  loss  of  carbon  may 
mean  gain  or  loss  of  either  carbohydrate  or  fat,  but  practically 
stored-up  carbon  generally  stands  for  accumulated  fat;  and, 
correspondingly,  loss  of  carbon  represents  a  withdrawal  from 
the  store  of  adipose  tissue,  since  glycogen  and  sugar  from  a 
quantitative  standpoint  figure  only  slightly  in  these  metabolic 
processes.  When  the  body  excretes  more  nitrogen  than  is 
taken  in  during  a  given  period,  there  is  only  one  interpreta- 
tion possible,  viz.,  that  the  body  is  losing  proteid  or  flesh. 
If,  on  the  other  hand,  the  nitrogen  import  exceeds  the  outgo, 
then  the  body  must  be  gaining  flesh.  Here,  again,  there  is 
the  theoretical  possibility  that  gain  or  loss  of  nitrogen  might 
represent  increase  or  decrease  of  proteid  in  some  glandular 
organ,  or  even  in  the  blood ;  but  practically  it  is  the  relatively 
bulky  muscle  tissue,  with  its  high  content  of  proteid  matter, 
that  is  most  subject  to  change  in  metabolism.  Finally,  it  is 
easy  to  see  how,  knowing  the  percentage  of  nitrogen  in  pro- 
teid and  the  percentage  of  carbon,  in  fat,  one  can  calculate 
from  the  nitrogen  and  carbon  lost  or  gained  the  amounts  of 
proteid  or  fat  added  to  the  capital  stock,  or  withdrawn  from 
the  store  of  nutritive  material. 

When  there  is  no  income,  as  in  fasting,  the  body  loses 
rapidly,  living  during  the  hunger  period  upon  its  store  of 
energy-containing  material.  Many  careful  observations  have 
been  made  upon  people  who  have  fasted  for  long  periods, 
some  as  long  as  thirty  days,  the  income  consisting  solely  of 


80 


THE  NUTRITION  OF  MAN 


water.     The  following  figures 1  show  the  daily  excretion  of 
nitrogen  in  several  notable  cases: 


Day  of  Fasting. 

Breithaupt. 
59.9  Kilos. 

Cetti. 
56.5  Kilos. 

Sued. 
62.4  Kilos. 

0 

grams 
13.0 

grams 
13.5 

grams 
16.2 

1 

10.0 

13.6 

13.8 

2 

9.9 

12.6 

11.0 

3 

13.3 

13.1 

13.9 

4 

12.8 

12.4 

12.8 

5 

11.0 

10.7 

12.8 

6 

9.9 

10.1 

101 

7 

10.9 

9.4 

8 

8.9 

8.4 

9 

10.8 

7.8 

10 

9.5 

6.7 

In  Succi's  case,  the  fasting  was  continued  for  thirty  days. 
The  daily  average  loss  of  nitrogen  from  the  llth  to  the  15th 
day  was  5.8  grams;  from  the  16th  to  the  20th  day,  5.3  grams; 
from  the  20th  to  the  25th  day,  4.7  grams;  and  from  the  26th 
to  the  30th  day,  5.3  grams.  A  daily  loss  of  5.3  grams  of 
nitrogen  means  a  breaking  down,  or  using  up,  of  33  grams  of 
proteid,  or  a  little  more  than  one  ounce.  On  the  sixth  day 
of  fasting,  all  three  of  these  subjects  showed  essentially  the 
same  daily  loss  of  nitrogen;  viz.,  10  grams,  which  implies  a 
using  up  of  62.5  grams  of  proteid  material.  We  must  not 
be  led  astray  by  these  figures,  however,  or  draw  too  hasty 


1  Taken  from  Landergren :  Untersuclmngen  iiber  die  Eiweissumsetzung  des 
Menschen.  Skandinavisches  Arcliiv  fur  Physiologie,  Band  14,  p.  112;  and 
from  A.  Magnus-Levy  :  v.  Noorden's  Handbuch  der  Pathologie  des  Stoffwech- 
sels,  1906,  p.  312. 


THE  BALANCE  OF  NUTBITION  81 

conclusions  therefrom  regarding  the  requirements  of  the  body 
for  proteid  food.  Noting  the  close  agreement  in  the  nitrogen 
output  of  the  three  subjects  on  the  sixth  day,  combined  with 
the  fact  that  their  body-weight  was  essentially  the  same,  we 
might  infer  that  62.5  grams  of  proteid  matter  represents  the 
amount  of  nitrogenous  food  necessary  to  maintain  nitrogen 
equilibrium  and  keep  the  body  in  a  condition  of  balance. 
Such  a  conclusion,  however,  would  be  quite  erroneous  for 
several  reasons.  First,  a  man  fasting,  if  he  was  in  an  ordi- 
nary condition  of  nutrition  prior  to  the  fast,  has  in  his  tissues 
a  large  store  of  fat.  It  is  considered  that  in  fasting  only 
about  10-12  per  cent  of  the  total  energy  of  the  body  is  de- 
rived from  tissue  proteid ;  the  major  part  comes  from  the  fat 
stored  up.  When  there  is  no  income  to  make  good  the  loss, 
the  body  must  naturally  draw  upon  its  own  store,  A  certain 
amount  of  proteid  must  be  used  up  daily,  but  in  addition 
there  are  the  energy  requirements  to  be  considered.  These 
are  met  mainly  by  fat  and  carbohydrate,  and  so  long  as  fat 
endures  proteid  will  be  drawn  upon  only,  or  mainly,  to  meet 
the  nitrogen  requirement;  but  if  the  fat  gives  out,  then  pro- 
teid must  be  used  in  larger  quantity,  as  a  source  of  energy. 
Hence  in  fasting,  the  daily  loss  of  nitrogen  will  be  governed 
largely  by  the  condition  of  the  body  as  regards  fat.  Thus, 
Munk  has  reported  the  case  of  a  well -nourished  and  fat  per- 
son, suffering  from  disease  of  the  brain,  who  gave  off  daily  in 
the  later  stages  of  starvation  only  one-third  the  amount  of 
nitrogen  voided  by  Cetti,  who  had  been  poorly  nourished. 
Obviously,  in  fasting,  as  soon  as  the  adipose  tissue  of  the  body 
has  been  largely  used  up,  there  will  be  an  increase  in  the 
amount  of  tissue  proteid  consumed,  since  under  such  condi- 
tions the  heat  of  the  body  and  the  energy  of  muscular  work 
(work  of  the  heart  and  involuntary  muscles)  must  come  from 
the  decomposition  of  proteid.  In  harmony  with  this  state- 
ment, it  is  frequently  observed  that  in  cases  of  starvation 

6 


82 


THE  NUTRITION  OF  MAN 


there  comes  toward  the  end  a  sudden  and  marked  increase 
in  the  output  of  nitrogen. 

Secondly,  the  elimination  of  nitrogen  during  the  earlier 
days  of  fasting  is  governed  in  large  measure  by  the  character 
and  extent  of  the  diet  on  the  days  just  preceding  the  fast. 
This  is  well  illustrated  by  some  experiments  conducted  by 
C.  Voit  on  a  dog.  In  the  first  series  of  experiments,  the  dog 
•  received  daily  2500  grams  of  meat  prior  to  fasting;  in  the 
second  series,  1500  grams  of  meat  were  fed  daily  before  the 
fast ;  while  in  the  third  series,  a  mixed  diet  relatively  poor  in 
proteid  was  given.  The  following  figures 1  show  the  amounts 
of  proteid  used  up  by  the  dog  (calculated  from  the  nitrogen 
excreted)  each  day  of  the  fasting  period,  under  the  different 
conditions : 


First  Series. 

Second  Series. 

Third  Series. 

First  fasting  day 

grams 
175 

grams 

77 

grams 
40 

Second    "        " 

72 

54 

33 

Third     « 

56 

46 

30 

Fourth  " 

50 

53 

36 

Fifth       " 

36 

43 

35 

Sixth      " 

39 

37 

37 

We  see  very  clearly  in  these  experiments  the  effects  of 
the  large  quantities  of  proteid  fed  on  the  destruction  of 
proteid  in  the  early  days  of  fasting.  When  the  body  is  rich 
in  proteid  from  food  previously  taken,  the  metabolism  of  ni- 
trogenous matter  is  very  large  at  first,  as  in  the  first  series 
of  experiments.  Indeed,  in  this  series,  even  on  the  fifth  day  of 


1  Expressed  in  this  form  from  Voit's  figures  by  A.  Magnus-Levy.    Loc.  cit., 
p.  311. 


THE   BALANCE   OF  NUTKITION  83 

fasting,  the  amount  cf  proteid  metabolized  was  larger  than 
on  the  second  day  of  the  third  series.  We  have  here  a  forci- 
ble illustration  of  the  physiological  axiom  that  excess  of  pro- 
teid matter  in  the  tissues,  or  in  the  blood,  stimulates  proteid 
metabolism ;  and  it  affords  convincing  proof  of  the  contention 
that  in  the  first  days  of  fasting  the  output  of  nitrogen,  or  the 
amount  of  proteid  used  up,  will  depend  in  large  measure  upon 
the  proteid  condition  of  the  body  at  the  time  of  the  fast. 
Equally  noticeable  is  the  fact  that  there  comes  a  time  —  the 
sixth  day  in  the  above  experiment  —  when  the  nitrogen  out- 
put reaches  a  common  level,  irrespective  of  the  previous  pro- 
teid condition  of  the  body.  Further,  it  is  easy  to  see  that 
the  greater  loss  of  nitrogen,  i.  e.,  the  large  breaking  down  of 
proteid  during  the  first  few  days  of  fasting,  in  those  cases 
where  proteid  food  has  been  freely  taken,  suggests  the  exist- 
ence in  the  tissues  of  two  forms  of  proteid.  We  may  term 
them,  following  the  nomenclature  of  Voit,  as  circulating  and 
morphotic,  or  tissue,  proteid ;  or,  we  may  designate  them  as 
labile  and  stable  forms  of  proteid.  In  other  words,  follow- 
ing the  usually  accepted  view,  this  circulating  or  labile  pro- 
teid represents  reserve  or  surplus  material  which  is  easily 
decomposed  and  hence  rapidly  gotten  rid  of,  while  the  stable 
proteid  is  more  slowly  oxidized,  and  its  metabolism  may  be 
taken  as  representing  more  nearly  the  real  necessities  of  the 
body.  However  this  may  be,  it  is  plainly  manifest  that  the 
nitrogen  output,  meaning  the  metabolism  of  proteid  matter, 
during  hunger  or  fasting  is  modified  by  a  variety  of  circum- 
stances, notably  the  previous  nutritive  condition  of  the  body 
as  regards  both  fat  and  proteid.  It  is  hardly  necessary  to 
add  that  the  amount  of  muscular  work  performed  is  another 
factor  of  importance  in  this  connection.  Fat  in  the  body 
represents  inert  material  stored  up  mainly  for  nutritive  pur- 
poses ;  hence,  in  hunger  it  is  used  largely,  and  serves  to  pro- 
tect more  important  tissues,  Thus,  experiments  have  shown 


84 


THE  NUTRITION   OF   MAN 


that  in  long  periods  of  fasting,  adipose  tissue  may  be  consumed 
to  the  extent  of  97  per  cent  of  the  total  amount  present, 
while  the  heart  and  nervous  tissue  will  not  lose  over  3  per 
cent  of  their  tissue  substance.  The  influence  of  tissue  fat 
upon  the  consumption  of  proteid  during  hunger  can  thus  be 
fully  appreciated. 

The  output  of  carbon  during  fasting  may  be  illustrated  by 
the  following  experiment1  made  upon  a  young  man,  the  nitro- 
gen data  being  included  for  comparison,  and  likewise  the  in- 
take of  food,  in  terms  of  nitrogen  and  carbon,  preceding  the 
fast  and  for  two  days  following  the  fast.  The  fasting  was  of 
five  days'  duration. 


Day. 

Body-weight. 

Intake. 

Output. 

Carbon. 

Nitrogen. 

Carbon.* 

Nitrogen. 

2 

kilos 

67.4 

grama 

438.7 

grama 
30.96 

grams 
303.4 

grams 
25.81 

3 

66.9 

0 

0 

197.6 

12.17 

4 

65.7 

0 

0 

188.8 

12.85 

5 

64.8 

0 

0 

183.2 

13.61 

6 

63.9 

0 

0 

180.8 

13.69 

7 

63.1 

0 

0 

176.2 

11.47 

8 

63.9 

439.9 

35.65 

270.5 

26.83 

9 

65.5 

391.7 

23.68 

258.8 

19.46 

On  the  non-fasting  days,  the  intake  consisted  of  an  ordi- 
nary food  mixture  of  proteids,  fats,  and  carbohydrates,  with 
a  small  addition  of  alcohol.  The  point  to  be  emphasized 


1  Taken  from  Johansson,  Landergren,  Sonde'n,  and  Tiegerstedt:   Beitrage 
zur  Kenntniss  des  Stoff  wechsels  beim  hungernden  Menschen.     Skandinavisches 
Archiv  fiir  Physiologie,  Band  7,  p.  29. 

2  The  carbon  output  represents  the  total  carbon  of  the  expired  air,  urine,  and 
excrement. 


THE  BALANCE   OF  NUTRITION  85 

here,  however,  is  that  the  carbon-content  was  more  than 
sufficient  to  meet  the  needs  of  the  body.  Thus,  it  will  be 
observed  that  on  all  three  of  the  days  when  food  was  taken, 
the  income  of  carbon  was  far  in  excess  of  the  output.  In 
other  words,  on  the  day  preceding  the  beginning  of  the  fast 
the  body  stored  up  135  grams  of  carbon,  and  on  the  day  fol- 
lowing the  fast  the  body  retained  169  grams  of  carbon  to 
help  make  good  the  loss.  Similarly,  the  amount  of  proteid 
food  taken  in  on  the  day  prior  to  the  fast  was  considerably 
in  excess  of  the  needs  of  the  body,  5.1  grams  of  nitrogen 
equivalent  to  31.8  grains  of  proteid  being  stored  for  future 
use.  Plainly,  the  man  was  not  in  either  carbon  or  nitrogen 
balance  prior  to  the  fast,  but  was  taking  far  more  food  than 
the  needs  of  the  body  called  for.  This  fact  may  be  empha- 
sized by  noting  that  the  total  fuel  value  of  the  daily  food, 
plus  the  fuel  value  of  the  alcohol,  amounted  on  an  average 
to  about  4200  large  calories,  while  the  fuel  value  of  the 
material  metabolized  on  the  feeding  days  averaged  only  2500 
calories.  Looking  at  the  figures  showing  the  output  of 
carbon,  as  well  as  of  nitrogen,  during  the  fasting  days,  it  is  to 
be  seen  that  in  the  early  days  of  fasting,  the  metabolism  of 
the  body  tends  to  remain  at  a  fairly  constant  level,  especially 
when  figured  per  kilogram  of  body- weight. 

To  fully  appreciate  what  takes  place  in  a  man  of  the  above 
body- weight  fasting  for  five  days  (though  living  on  a  large 
excess  of  food  prior  to  the  fast),  the  daily  losses  of  carbon 
and  nitrogen  may  be  translated  into  terms  of  fat  and  proteid. 
If  it  is  assumed  that  the  total  carbon,  aside  from  what  neces- 
sarily belongs  to  the  proteid  indicated  by  the  nitrogen  figures, 
comes  from  the  oxidation  of  fat,  it  is  easy  to  compute  the 
amounts  of  fat  and  proteid  metabolized,  or  destroyed,  each 
day  of  the  fasting  period  These  are  shown  in  the  following 
table: 


THE  NUTRITION  OF  MAN 


Day. 

Proteid 
metabolized. 

Fat 
metabolized. 

3 

grams 
76.1 

grams 
206.1 

4 

80.3 

191.6 

5 

85.1 

181.2 

6 

85.6 

177.6 

7 

71.7 

181.2 

Finally,  if  from  these  figures  we  calculate  the  fuel  value 
of  the  proteid  and  fat  oxidized  per  day,  it  is  possible  to  gain 
a  fairly  clear  conception  of  the  part  played  by  these  two 
classes  of  tissue  material  during  fasting,  in  furnishing  the  heat 
of  the  body  and  the  energy  for  muscular  motion,  etc. 


Day. 

Fuel  Value  of 
the  Proteid 
metabolized. 

Fuel  Value  of 
the  Fat 
metabolized. 

Total 
Fuel  Value. 

calories 

calories 

calories 

3 

303 

1916 

2220 

4 

320 

1781 

2102 

6 

339 

1684 

2024 

6 

341 

1651 

1992 

7 

286 

1684 

1970 

These  somewhat  general  statements,  with  the  illustrations 
given,  will  serve  in  a  brief  way  to  emphasize  some  of  the 
essential  features  of  metabolism  in  the  fasting  individual; 
where  there  is  no  income  of  energy-containing  material,  and 
where  the  body  must  draw  entirely  upon  its  store  of  accumu- 
lated fat  and  proteid  to  keep  the  machinery  in  motion,  main- 
tain body  temperature,  and  do  the  tasks  of  every-day  life. 
When  it  is  remembered  that  persons  have  fasted  for  periods 


THE  BALANCE  OF  NUTRITION  87 

of  thirty  days  or  longer  without  succumbing,  it  is  evident 
that  the  body  of  the  well-nourished  man  has  a  large  reserve 
of  nutritive  material,  which  can  be  drawn  upon  in  cases  of 
emergency.  At  the  same  time,  the  facts  presented  show  us 
that  in  the  early  days  of  fasting  the  actual  amounts  of  tissue 
proteid  and  body  fat  consumed  are  not  large.  In  Cetti's 
case,  on  the  sixth  day  of  fasting  the  metabolized  nitrogen 
amounted  to  10  grams,  which  implies  a  loss  of  62.5  grams  of 
proteid.  At  this  rate  of  loss,  one  pound  of  dry  proteid 
matter  in  the  form  of  tissue  proteid  would  meet  the  wants 
of  a  man  of  130  pounds  body-weight  for  seven  and  a  half 
days,  provided  of  course  there  was  a  reasonable  stock  of  fat 
to  help  satisfy  the  energy  requirements.  Finally,  we  may 
again  emphasize  the  fact  that  the  loss  of  nitrogen  in  the  fast- 
ing man  is  by  no  means  a  measure  of  the  minimal  proteid 
requirement.  By  feeding  fat,  or  carbohydrate,  or  both,  the 
output  of  nitrogen  can  be  materially  diminished,  although 
naturally  we  cannot  establish  a  nitrogen  balance  by  so  doing, 
since  the  income  is  free  from  nitrogen;  but  we  can  postpone 
for  a  time  the  approach  of  nitrogen  starvation. 

We  may  next  profitably  consider  the  effect  of  a  pure  pro- 
teid diet  —  such  as  lean  meat  free  from  fat  —  on  the  output 
of  nitrogen.  In  studying  this  problem,  we  at  once  meet  with 
several  important  and  surprising  facts.  First,  we  are  led  to 
see  that,  strange  as  it  may  seem,  every  addition  of  proteid 
to  the  diet  results  in  an  increased  excretion  of  nitrogen.  In 
other  words,  increase  of  proteid  income  is  followed  at  once 
by  an  increase  in  the  metabolism  of  proteid,  with  a  corre- 
sponding outgo  of  nitrogen.  The  hungry  or  fasting  man 
with  his  income  entirely  cut  off,  and  consequently  suffering 
from  a  heavy  drain  upon  his  capital  stock,  would  be  expected, 
when  suddenly  supplied  with  fresh  capital  in  the  form  of 
meat  or  other  kind  of  proteid  food,  to  hold  on  firmly  to  this 
all-important  foodstuff;  but  such  is  not  the  case.  It  is  im- 


88  THE   NUTRITION  OF  MAN 

possible,  for  example,  to  establish  nitrogen  equilibrium  by 
an  income  of  proteid  equal  to  what  the  individual  during 
fasting  is  found  to  metabolize.  As  stated  by  another,  "  It  is 
one  of  the  cardinal  laws  of  proteid  metabolism  that  the  store 
of  nitrogenous  substances  in  the  body  is  not  increased  by,  or 
not  in  proportion  to,  an  increase  in  the  nitrogen  intake." 
The  principle  is  well  illustrated  in  the  fasting  experiment 
just  described.  On  the  fifth  day  of  fasting,  the  nitrogen  out- 
put amounted  to  11.4  grams.  On  the  day  following,  the  man 
took  35.6  grams  of  nitrogen  in  the  form  of  proteid,  while  the 
excretion  of  nitrogen  for  that  day  rose  to  26.8  grams.  In 
other  words,  although  deprived  of  all  proteid  income  for  five 
days,  and  during  that  period  drawing  entirely  upon  his  proteid 
capital,  the  man  was  wholly  unable  to  avail  himself  of  the 
proteid  so  abundantly  supplied  at  the  close  of  the  fast  and 
make  good  the  losses  of  the  preceding  days;  only  a  small 
proportion  of  the  proteid  income  could  be  retained.  If  a  dog 
fed  on  a  definite  quantity  of  meat  suddenly  has  his  proteid 
income  increased,  there  is  at  once  an  acceleration  of  proteid 
metabolism,  and  a  corresponding  increase  in  the  output  of 
nitrogen.  Addition  of  still  more  proteid  to  his  income  is 
followed  by  an  accumulation  of  a  portion  of  the  proteid ;  but 
this  tends  to  decrease  gradually,  while  there  is  a  correspond- 
ing daily  increase  in  the  excretion  of  nitrogen.  In  this 
manner,  there  finally  results  a  condition  of  nitrogenous  equi- 
librium or  nitrogen  balance. 

Again,  an  animal  brought  into  nitrogen  equilibrium  by 
excessive  proteid  feeding,  if  suddenly  given  a  small  amount 
of  meat  per  day,  tends  to  put  out  nitrogen  from  its  own 
tissues.  This  tissue  loss,  however,  decreases  slowly,  and 
eventually  the  animal  is  quite  likely  to  re-establish  nitrogen 
equilibrium  at  a  lower  level.  There  is,  in  other  words, 
a  strong  tendency  for  the  body  to  pass  into  a  condition 
of  nitrogen  balance  under  different  conditions  of  proteid 


THE  BALANCE   OF  NUTKITION  89 

feeding,  even  after  a  long  period  of  nitrogen  loss  and  with 
an  abundance  of  proteid  in  the  intake.  The  starving  body, 
as  we  have  seen,  cannot  make  use  of  all  the  nitrogen  fed, 
although  we  can  well  conceive  its  great  need  for  all  the  pro- 
teid available.  A  certain  amount  of  the  proteid  fed,  or  its 
contained  nitrogen,  is  at  once  passed  out  of  the  body  and  lost, 
even  though  the  organism  be  gasping,  as  it  were,  for  proteid 
to  make  good  the  drain  incidental  to  long  fasting.  A  recent 
writer l  has  suggested  that  some  explanation  for  these  anom- 
alies may  be  found  in  the  supposition  "  that  a  long  succession 
of  generations  in  the  past,  which  have  lived  from  choice  or 
necessity  on  a  diet  rich  in  proteids,  have  handed  down  to  us, 
as  an  inheritance,  a  constitution  in  which  arrangements  exist 
for  the  removal  of  nitrogen  from  a  considerable  part  of  this 
proteid.  The  fact  that  the  amount  of  proteid  taken  is  re- 
adjusted to  suit  the  actual  needs  of  the  body,  though  it 
makes  these  arrangements  unnecessary,  will  not  necessarily 
remove  them.  The  denitrifying  enzyme,  which  has  been 
trained  to  keep  guard  over  the  entrances  by  which  nitroge- 
nous substances  are  admitted  into  the  body,  will  continue 
to  levy  its  toll  of  nitrogen,  even  when  the  amount  of  proteid 
presented  to  it  is  no  more  than  the  tissues  which  it  serves 
actually  require." 

As  an  illustration  of  how  the  body  behaves  with  a  low 
nitrogen  intake  followed  by  a  sudden  increase  in  the  income 
of  proteid,  some  data  from  an  experiment  performed  by 
Sive*n2  on  himself  may  be  cited: 


1  Leathes :  Problems  in  Animal  Metabolism.     Philadelphia,  1906,  p.  157. 

2  Siven :  Zur  Kenntniss  des  Stoffweehsels  beim  erwachsenen  Menschen,  mit 
besonderer  Beriicksichtigung  des  Eiweissbedarfs.     Skandinavisehes  Archiv  fiir 
Physiologie,  Band  11,  p.  308. 


90 


THE  NUTKITION  OF  MAN 


Date. 

Body-weight. 

Nitrogen  of 
the  Food. 

Nitrogen 
excreted. 

Nitrogen 
Balance. 

kilos 

grams 

grams 

grams 

Nov.    6 

65.4 

2.69 

8.31 

-5.62 

7 

65.4 

2.69 

5.37 

-2.68 

8 

65.1 

2.69 

5.71 

-3.02 

9 

65.3 

2.69 

4.88 

-2.19 

10 

65.0 

2.69 

4.32 

-1.63 

11 

64.9 

2.69 

4.25 

-1.56 

12 

64.9 

2.69 

4.47 

-1.78 

13 

64.6 

2.96 

4.88 

-1.92 

14 

64.4 

2.96 

4.30 

-1.44 

15 

64.3 

2.96 

4.75 

-1.79 

16 

64.4 

2.96 

4.36 

-1.40 

17 

64.4 

2.96 

4.13 

-1.17 

18 

64.4 

2.96 

4.35 

-1.39 

19 

64.4 

2.96 

4.32 

-1.36 

20 

64.4 

2.96 

4.22 

-1.26 

21 

64.0 

2.96 

4.06 

-1.10 

-  31.31 

22 

64.1 

4.02 

4.22 

-0.20 

23 

64.4 

4.02 

4.35 

-0.33 

24 

64.4 

4.02 

4.21 

-0.19 

25 

64.4 

4.02 

4.40 

-0.38 

-1.10 

26 

64.2 

8.24 

6.56 

+  1.68 

27 

64.4 

13.45 

8.67 

+  4.78 

28 

64.4 

13.66 

10.54 

+  3.12 

29 

64.0 

13.45 

11.10 

+  2.35 

30 

64.2 

13.24 

12.83 

+  0.41 

Dec.    1 

64.2 

13.24 

11.70 

+  1.54 

2 

63.9 

12.61 

12.00 

+  0.61 

+  14.49 

3 

64.0 

22.93 

16.24 

+  6.69 

4 

63.9 

22.41 

21.47 

+  0.94 

5 

63.9 

22.41 

23.10 

-0.69 

6 

63.6 

23.35 

23.12 

+  0.23 

7 

63.9 

23.04 

22.82 

+  0.22 

8 

63.8 

22.62 

22.86 

-0.24 

+  6.15 

THE  BALANCE   OF  NUTRITION  91 

I  have  ventured  to  give  these  data  in  some  detail,  because 
of  their  exceeding  great  interest  in  several  directions  aside 
from  the  point  under  discussion.  Confining  our  attention  to 
the  nitrogen  exchange,  it  is  to  be  observed  that  for  a  period 
of  two  weeks  Sive'n  lived  on  less  than  3  grams  of  nitrogen 
per  day,  and  without  any  excessive  intake  of  carbohydrate  or 
fat.  During  this  time,  the  body  naturally  was  in  a  condition 
of  minus  balance  as  regards  nitrogen,  the  output  being  con- 
siderably larger  than  the  income.  The  total  amount  of  nitro- 
gen lost  in  the  period,  31  grams,  corresponds  to  a  breaking 
down  of  193  grams  of  tissue  proteid,  or  over  one-third  of  a 
pound.  On  increasing  the  income  of  nitrogen  to  4  grams  per 
day,  the  nitrogen  loss  still  continued,  though  at  a  much  lower 
rate ;  indeed,  the  body  is  seen  to  approach  very  closely  to  a 
condition  of  nitrogen  equilibrium.  Still  further  increase  of 
the  nitrogen  income  to  13  grams  per  day  was  followed  at  once 
by  a  slight  accumulation  of  proteid,  and  the  body  showed  a 
decided  plus  balance  of  nitrogen,  as  on  November  27.  This, 
however,  is  seen  to  decrease  gradually  with  a  corresponding 
daily  increase  in  the  outgo  of  nitrogen,  until  on  December  2 
the  body  was  once  more  practically  in  nitrogenous  equilibrium. 
On  again  increasing  the  nitrogen  income,  to  23  grams  per  day, 
the  same  process  was  repeated,  although  in  this  case  the  body 
more  quickly  approached  a  condition  of  nitrogen  balance. 

We  see  in  these  data  striking  confirmation  of  the  statement 
that  the  nitrogen  outgo  tends  to  keep  pace  with  the  income 
of  nitrogen,  the  body  always  striving  to  maintain  a  condition 
of  nitrogen  equilibrium.  Consequently,  the  fasting  man  hav- 
ing lost  largely  of  his  store  of  proteid  can  replace  the  latter 
only  slowly,  even  though  he  eats  abundantly  of  proteid  food. 
Thus,  Sive'n  in  the  week  ending  December  2,  though  taking 
over  13  grams  of  nitrogen  a  day,  retained  in  his  body  only  14.5 
grams  of  nitrogen  during  the  entire  seven  days ;  while  in  the 
six  days  following,  with  a  daily  intake  of  23  grams  of  nitro- 


92  THE  NUTRITION   OF  MAN 

gen,  he  gained  only  about  8  grams  additional.  The  human 
body  does  not  readily  store  up  proteid,  and  this  is  true  no  matter 
how  greatly  the  tissues  are  in  need  of  replenishment. 

If  the  daily  income  is  reinforced  by  the  addition  of  carbo- 
hydrate or  fat,  there  is  observed  a  decided  influence  on  the 
outgo  of  nitrogen;  the  rate  or  extent  of  proteid  metabolism 
is  at  once  modified,  fat  and  carbohydrate  both  having  a  direct 
saving  effect  on  proteid.  Neither  fat  nor  carbohydrate  can 
prevent  the  katabolism  of  proteid,  but  they  can  and  do  de- 
crease it,  and  thus  serve  as  proteid-sparers.  In  the  fasting 
body,  or  where  there  is  only  an  intake  of  proteid,  the  latter 
material,  except  for  the  fat  contained  in  the  tissues,  must 
serve  the  double  purpose  of  meeting  the  specific  nitrogen  re- 
quirements of  the  body  and  furnishing  the  requisite  energy. 
The  energy  requirements,  however,  can  be  met  more  advan- 
tageously by  either  of  the  non-nitrogenous  foodstuffs,  and 
just  so  far  as  they  are  oxidized,  so  far  will  there  be  a  saving 
of  proteid.  Herein  lies  the  philosophy  of  a  mixed  diet,  with 
its  natural  intermingling  of  proteid,  fat,  and  carbohydrate. 
For  the  same  reason,  the  body  of  a  man  rich  in  fat  will  in 
fasting  lose  far  less  proteid  per  day  than  the  lean  man ;  or, 
if  fed  with  a  given  amount  of  proteid  food,  the  fat  man  may 
attain  nitrogen  equilibrium,  or  even  store  up  a  little  proteid, 
while  on  the  same  diet  the  lean  man  will  lose  proteid.  Fur- 
ther, if  a  man  is  in  nitrogen  balance  with  a  given  amount  of 
proteid  food,  the  addition  of  fat  or  carbohydrate  to  the  diet 
will  permit  of  a  reduction  in  the  amount  of  proteid  necessary 
to  maintain  nitrogenous  equilibrium.  Fat,  however,  when 
added  to  food,  does  not  always  protect  proteid  to  the  extent 
possibly  suggested  by  the  preceding  statements.  The  follow- 
ing data  from  oft-quoted  experiments  by  Voit l  on  dogs  will 
serve  to  illustrate: 


1  C.  Voit :  Hermann's  Handbuch  der  Physiologie  des  Gesammtstoff wechsela, 
Band  6,  p.  130. 


THE   BALANCE   OF  NUTEITION 


93 


Food. 

Flesh. 

Meat. 

Fat. 

Metabolized. 

On  the  Body. 

grams 
1500 

grama 

0 

grams 
1512 

grams 
-  12 

1500 

150 

1474 

+  26 

500 

0 

556 

-56 

500 

100 

520 

-20 

It  is  to  be  observed  that  in  both  of  these  experiments  the 
fairly  large  addition  of  fat  results  in  a  saving  of  proteid,  but 
the  sparing  effect  in  the  first  experiment  amounts  to  only  38 
grams  of  proteid  for  the  150  grams  of  fat  added.  In  the 
second  experiment,  however,  there  is  a  saving  of  36  grams  of 
proteid,  although  only  100  grams  of  fat  were  fed.  The  radi- 
cal point  of  difference  in  the  two  experiments  is  the  amount 
of  proteid  ingested.  Proteid  food  stimulates  proteid  metabo- 
lism; it  likewise  accelerates  the  metabolism  of  non-nitroge- 
nous matter,  consequently  the  sparing  or  protecting  effect  of 
fat  on  proteid  is  most  conspicuous  when  the  intake  of  pro- 
teid is  relatively  small.  Only  under  such  conditions,  does  fat 
protect  in  large  degree  the  consumption  of  proteid  in  the 
body.  In  the  ordinary,  daily,  dietary  of  man,  with  its  great 
variety  of  food  materials  and  with  its  proteid-content  not 
exceeding  125  grams,  fat  is  apt  to  be  a  conspicuous  element, 
and  under  such  conditions  its  sparing  effect  on  proteid  me- 
tabolism is  most  marked.  Further,  it  must  not  be  forgotten, 
as  Voit  originally  pointed  out,  that  the  adipose  tissue  of  the 
body  acts  like  the  food-fat,  and  consequently  the  proteid- 
sparing  effect  of  the  former  may  be  added  to  that  of  the 
latter. 

The  addition  of  carbohydrate  to  a  meat  diet  produces  at 


THE  NUTRITION  OF  MAN 


once  a  saving  in  the  decomposition  of  proteid,  as  shown  in 
the  following  figures,  covering  an  experiment  of  two  days : 


Meat. 
600  grams. 

500 


Sugar. 
200  grams. 


Proteid  metabolized. 
502  grams. 

564 


Without  the  sugar,  there  was  a  minus  balance  of  64  grams 
of  proteid,  but  addition  of  the  carbohydrate  caused  practi- 
cally a  saving  of  all  of  this,  with  establishment  of  essentially 
a  nitrogen  balance.  The  sparing  of  proteid  by  carbohydrate 
is  greater  than  by  fats,  a  fact  of  considerable  dietetic  impor- 
tance which  is  well  illustrated  by  the  following  experiments 
(on  dogs)  taken  from  Voit: 


Food. 

Flesh. 

Meat. 

Non-nitrogenous  Food. 

Metabolized. 

Balance  of  the  Body. 

grams 
500 

grama 

250  Fat 

grams 
558 

grams 
-58 

500 

300  Sugar 

466 

+34 

600 

200  Sugar 

605 

-5 

800 

250  Starch 

745 

+55 

800 

200  Fat 

773 

+27 

2000 

200-300  Starch 

1792 

+208 

2000 

250  Fat 

1883 

+117 

In  considering  the  results  of  this  experiment,  it  must  be 
remembered  that  the  calorific  or  fuel  value  of  fat  as  compared 
with  carbohydrate  is  as  9.3  :  4.1;  in  other  words,  fats  have 
a  fuel  value  of  more  than  twice  that  of  carbohydrates.  In 
spite  of  this  fact,  it  is  clearly  evident  that  carbohydrates  as 
a  class  —  for  the  different  sugars  and  starches  act  alike  in 
this  respect  —  are  far  more  efficient  than  fats  in  saving  pro- 
teid. Thus,  with  an  income  of  500  grams  of  meat  and  250 


THE  BALANCE   OF  NUTRITION  95 

grams  of  fat,  the  body  of  the  animal  lost  58  grams  of  proteid, 
while  with  a  like  amount  of  meat  and  300  grams  of  sugar  the 
body  not  only  saved  the  58  grams,  but  in  addition  stored  34 
grams  of  proteid,  showing  a  plus  balance  to  that  extent.  The 
sparing  of  proteid  by  carbohydrate  amounts  on  an  average, 
according  to  Voit,  to  9  per  cent  —  in  the  highest  cases  to  15 
per  cent  —  of  the  proteid  given,  while  the  saving  produced 
by  fat  averages  only  7  per  cent.  Futher,  increasing  quanti- 
ties of  carbohydrates  in  the  food  diminish  the  rate  of  proteid 
metabolism  much  more  regularly  and  constantly  than  in- 
creasing quantities  of  fat.  We  may  attribute  this  difference 
in  action,  in  a  measure  at  least,  to  the  greater  ease  in  oxi- 
dation and  utilization  of  the  carbohydrate.  In  any  event, 
starches  and  sugars  are  most  valuable  adjuncts  to  the  daily 
diet,  because  of  this  marked  proteid-saving  power,  while  their 
fuel  value  adds  just  so  much  to  the  total  energy  intake. 

A  more  striking  illustration  of  the  action  of  carbohydrate  in 
sparing  proteid  is  seen  in  experiments  on  man,  where  the 
nitrogen  intake  is  reduced  to  a  minimum,  so  as  to  constitute 
a  condition  of  specific  nitrogen-hunger.  In  such  a  case,  in- 
creasing amounts  of  carbohydrate  added  to  the  intake  reduce 
enormously  the  using  up  -of  tissue  proteid.  The  following 
experiment  with  a  young  man  22  years  old  and  71.3  kilos 
body-weight,  reported  by  Landergren,1  affords  good  evidence 
of  the  extent  to  which  this  proteid  sparing  power  may  mani- 
fest itself. 

We  see  here  the  nitrogen  consumption  fall  to  the  exceed- 
ingly low  level  of  3.34  grams  per  day,  or  0.047  gram  per  kilo 
of  body-weight.  To  appreciate  the  full  significance  of  this 
drop  in  the  extent  of  proteid  metabolism,  we  may  recall  that 
Succi,  with  a  body-weight  of  only  62. 4  kilos,  on  the  seventh 
day  of  fasting  excreted  9.4  grams  of  nitrogen,  corresponding 

1  Landergren :  Untersuchungen  iiber  die  Eiweissumsetzung  des  Menschen. 
Skandinavisches  Archiv  fiir  Physiologie,  Band  14,  p.  114. 


96 


THE  NUTRITION  OF  MAN 


Day. 

Intake. 

Output. 

Proteid 
metabo- 
lized. 

Proteid. 

Fat. 

Carbo- 
hydrate. 

Alcohol. 

Calories. 

Nitrogen 
of  Urine. 

1 

grams 
35.2 

grams 
6.1 

grams 

507 

grams 

26.6 

2465.9 

grams 
12.16 

grams 

76.0 

2 

28.7 

4.7 

787 

26.6 

3574.3 

8.37 

62.3 

3 

28.8 

4.7 

841 

26.6 

3796.1 

5.02 

31.3 

4 

28.3 

4.9 

839 

13.3 

3690.5 

4.50 

28.1 

5 

5.4 

898 

.... 

3703.9 

4.01 

25.0 

6 

6.0 

.. 

931 

.... 

3841.7 

3.36 

21.0 

7 

5.6 

•  • 

908 

.... 

3745.8 

3.34 

20.8 

to  a  metabolism  of  58.7  grams  of  tissue  proteid.  In  other 
words,  with  an  intake  of  only  5.6  grams  of  proteid,  the  addi- 
tion of  908  grams  of  carbohydrate,  with  a  total  fuel  value  of 
3745  calories,  reduced  the  consumption  of  tissue  proteid  to 
20.8  grams.  The  same  individual,  if  fasting,  would  un- 
doubtedly have  used  up  at  least  70  grams  of  tissue  proteid. 

It  is  evident  from  what  has  been  said  that  both  of  these 
non-nitrogenous  foods,  fat  and  carbohydrate,  play  a  very  im- 
portant part  in  nutrition,  because  of  their  ability  to  maintain 
in  a  measure  the  integrity  of  tissue  proteid.  When  we  recall 
that  a  diet  of  pure  proteid,  such  as  meat  or  eggs,  must  be 
excessive  in  quantity  in  order  to  meet  the  energy  require- 
ments of  the  body,  and  that  the  stimulating  action  of  proteid 
food  serves  to  whip  up  body  metabolism,  we  can  appreciate 
at  full  measure  the  great  physiological  economy  which  results 
from  the  addition  of  carbohydrate  and  fat  to  the  daily  diet. 
The  establishment  of  nitrogenous  equilibrium  is  made  pos- 
sible at  a  much  lower  level  by  the  judicious  addition  of  these 
two  non-nitrogenous  foodstuffs.  The  same  principle  may  be 
illustrated  in  another  way,  viz.,  by  noting  the  effect  on  tissue 


THE  BALANCE   OF  NUTKITION 


97 


proteid  of  withdrawal  of  a  portion  of  the  fat  or  carbohydrate 
of  the  intake,  in  the  case  of  a  person  nearly  or  quite  in  nitro- 
gen balance.  The  following  experiment l  affords  a  good  ex- 
ample of  what  will  occur  under  such  treatment : 


Income. 

Output  of 
Nitrogen. 

Balance  of 
Nitrogen 
in  Body. 

Nitrogen. 

Fat. 

Carbo- 
hydrate. 

Calories. 

Av.  of  3  days 

grams 

15.782 

grams 
40.47 

grams 
289.6 

1955 

grams 
14.927 

+0.862 

Nov.  30 

15.782 

40.34 

177.3 

1493 

14.959 

+0.830 

Dec.    1 

15.782 

40.34 

177.3 

1493 

17.546 

-1.757 

2 

15.782 

40.34 

177.3 

1493 

18452 

-2.663 

Average  of  the  last  two  days 

.     -2.210 

Starting  with  the  body  in  a  condition  of  plus  nitrogen 
balance,  i.  e.,  with  a  mixed  diet  more  than  sufficient  to  main- 
tain the  tissue  proteid  intact,  the  reduction  of  the  fuel  value 
of  the  food  from  1955  to  1493  calories  by  cutting  off  112 
grams  of  carbohydrate  per  day  was  followed  by  a  gradual, 
but  marked,  increase  in  the  output  of  nitrogen;  indicating 
thereby  the  extent  to  which  the  body  proteid  was  then  drawn 
upon  to  make  good  flie  loss  of  energy-containing  income. 
The  body  showed  at  the  close  of  the  experiment  a  minus 
nitrogen  balance  averaging  2.2  grams  per  day,  or  a  loss  of 
13.8  grams  of  tissue  proteid,  which  would  obviously  have 
continued,  under  the  above  conditions,  until  the  body  was 
exhausted.  In  other  words,  the  112  grams  of  carbohydrate, 
if  added  to  the  diet  on  December  3  and  the  following  days, 
would  have  quickly  saved  the  daily  loss  of  2.4  grams  of 
nitrogen,  and  thus  changed  the  drain  of  tissue  proteid  to  an 

1  An  experiment  by  Miura,  quoted  from  A.  Magnus-Levy  in  v.  Noorden's 
Handbuch  der  Pathologic  des  Stoff  wechsels,  1906,  p.  331. 

7 


98  THE  NUTBITION   OF  MAN 

actual  gain,  with  consequent  establishment  of  a  growing  plus 
balance. 

It  is  obvious  from  what  has  been  stated,  that  in  man  the 
body  can  accomplish  a  storing  of  proteid  only  when  the 
intake  is  reinforced  by  substantial  additions  of  fat  or  carbo- 
hydrate. It  is  plainly  a  matter  of  great  physiological  impor- 
tance that  the  body  should  be  able  to  increase  at  times  its 
reserve  of  proteid.  This,  however,  cannot  apparently  be 
accomplished  on  a  large  scale  under  ordinary  conditions. 
Any  storing  up  of  nutritive  material  in  excess,  whether  it 
be  proteid  or  fat,  necessarily  involves  overfeeding,  i.  <>.,  the 
taking  of  an  amount  of  food  beyond  the  capacity  of  the  body 
to  metabolize  at  the  time.  Fat,  as  we  know,  may  be  stored 
in  large  quantities,  and  it  is  in  cases  of  overfeeding  with 
non-nitrogenous  foods  that  we  find  accumulation  of  fat  most 
marked.  Overfeeding  with  proteid,  however,  does  not  lead 
to  corresponding  results,  owing  primarily  to  the  peculiar 
physiological  properties  of  proteid;  its  general  stimulating 
effect  on  metabolism,  the  tendency  of  the  body  to  establish 
nitrogenous  equilibrium  at  different  levels,  and  the  fact  em- 
phasized by  von  Noorden  that  flesh  deposition  is  primarily  a 
function  of  the  specific  energy  of  developing  cells.  In  other 
words,  the  protoplasmic  cells  of  the  body  are  more  important 
factors  in  the  storing  or  holding  on  to  proteid  than  an  excess 
of  proteid-containing  food. 

It  is  generally  considered  as  a  settled  fact,  that  in  man 
it  is  impossible  to  accomplish  any  large  permanent  storing 
or  deposition  of  flesh  by  overfeeding.  Similarly,  it  is  un- 
derstood that  the  muscular  strength  of  man  cannot  be  greatly 
increased  by  an  excessive  intake  of  food.  The  only  con- 
ditions under  which  there  is  ordinarily  any  marked  and 
permanent  flesh  deposition  are  such  as  are  connected  with 
the  regenerative  energy  of  living  cells.  Thus,  as  von 
Noorden  has  stated,  an  accumulation  or  storing  of  tissue 


THE  BALANCE  OF  NUTEITION  99 

proteid  is  seen  especially  in  the  growing  body,  where  new 
cells  are  being  rapidly  constructed ;  also  in  the  adult  where 
growth  may  have  ceased,  but  where  increased  muscular 
work  has  resulted  in  an  hypertrophy  or  enlargement  of  the 
muscular  tissue;  and  lastly  in  those  cases  where,  owing 
to  previous  insufficient  food  or  to  the  wasting  away  of  the 
body  incidental  to  disease,  the  proteid  content  of  the  tissues 
has  been  more  or  less  diminished,  and  consequently  an  abun- 
dance of  proteid  food  is  called  for  and  duly  utilized  to  make 
good  the  loss.  In  some  oft-quoted  experiments  by  Krug, 
conducted  on  himself,  it  was  observed  that  with  an  abundant 
food  intake,  sufficient  to  furnish  2590  calories  per  day  (44 
calories  per  kilo  of  body-weight),  a  condition  approaching 
nitrogenous  equilibrium  was  easily  maintained. '  On  then 
increasing  the  fuel  value  of  the  food  to  4300  calories  (71  calo- 
ries per  kilo  of  body-weight)  by  addition  of  fat  and  carbo- 
hydrate, there  was  during  a  period  of  fifteen  days  a  sparing 
of  49.5  grams  of  nitrogen  or  309  grams  of  proteid,  which 
would  correspond  to  about  1450  grams,  or  three  pounds,  of 
fresh  muscle.  It  is  to  be  noted,  however,  that  of  this  excess 
of  calories  added  to  the  intake  only  5  per  cent  was  made 
use  of  for  flesh  deposit,  the  remaining  95  per  cent  going  to 
make  fat. 

Again,  we  may  call  attention  to  the  well-known  fact  that 
in  feeding  animals  for  food,  while  fat  may  be  laid  on  in  large 
amounts,  flesh  cannot  be  so  increased  by  overfeeding.  In  this 
matter,  however,  race  and  individuality  count  for  considerable. 
Thus,  there  is  on  record  a  more  recent  series  of  experiments 
conducted  by  Dapper 1  on  himself  which  shows  some  remark- 
able results.  Starting  with  a  daily  diet  not  excessive  in 
amount,  he  was  able  by  an  addition  of  only  80  grams  of 
starch  to  accomplish  a  laying  up  of  3.32  grams  of  nitrogen 

1  Max  Dapper :  Ueber  Fleischmast  beim  Menschen.  Inaug.  Disser.  Mar- 
burg, 1902. 


100 


THE   NUTRITION   OF   MAN 


per  day  for  a  period  of  twelve  days,  or  a  total  gain  of  39.8 
grams  of  nitrogen,  equal  to  248  grams  of  proteid.  It  may  be 
said  that  the  gain  of  proteid  or  flesh  here  for  the  twelve  days 
was  no  greater  than  in  the  preceding  case  (fifteen  days),  but 
the  difference  lies  in  the  fact  that  Krug  accomplished  his 
gain  by  increasing  the  daily  intake  from  2590  to  4800  calo- 
ries, an  amount  which  he  found  too  large  to  be  eaten  with 
comfort,  while  the  later  investigator  raised  the  fuel  value 
of  his  daily  food  from  2930  to  only  3250  calories.  As  the 
experiments  by  Dapper  contain  other  points  of  interest  bear- 
ing on  the  question  before  us,  we  may  advantageously  con- 
sider them  somewhat  in  detail.  The  following  table  gives 
the  more  important  results: 


Food  Composition. 

No. 
of 
Exp. 

Dura- 
tion. 

Character 
of  Food. 

Nitrogen 
Balance. 

Maxima  and  Minima 
of  Nitrogen-gain. 

Nitrogen. 

Calories. 

days 

grams 

grams 

grams 

1 

6 

Ordinary   mixed 

20.25 

2930 

+2.18 

+3.2  on  4th  day. 

diet 

+1.5  on  6th  day. 

2 

12 

Ditto  +80  grams 

20.09 

3250 

+3.32 

+4.75  on  2d  day. 

starch 

+4.65  on  12  tli  day. 

+2.30  on  8th  day. 

3 

9 

Ditto  +  80  grams 

24.58 

3400 

+2.55 

+5.98  on  1st  dav. 

starch,  +  40 

+4.73  on  2d  day. 

grams  plasmon 

+0.50  on  6th  day. 

+1.60  on  9th  day. 

As  we  look  at  these  results,  the  nitrogen  gain  for  the  first 
arid  second  days  of  the  third  experiment  and  the  first  day  of 
the  second  experiment  may  well  attract  our  attention,  since 
they  show  an  astonishing  laying  by  of  proteid,  or  gain  of  flesh, 
under  the  influence  of  a  comparatively  small  increase  in  the 
fuel  value  of  the  food.  A  gain  of  5.98  grams  of  nitrogen 
means  37.3  grams  of  proteid,  or  more  than  an  ounce;  by  no 
means  an  inconsiderable  addition  for  one  day  to  the  store  of 
tissue  proteid.  In  the  third  experiment,  where  plasmon  (dried, 


THE  BALANCE   O 

milk  proteid)  was  added  to  the  diet,  there  is  to  be  noted  a 
gradual  falling  off  in  the  proteid-sparing  power,  which  may 
perhaps  be  interpreted  as  implying  that  the  body  was  prac- 
tically saturated  with  proteid,  and  that  owing  to  this  fact  the 
body  was  unable  to  continue  its  laying  hold  of  nitrogen.  In 
the  entire  period  of  21  days,  however,  the  body  had  suc- 
ceeded in  accumulating  a  store  of  62.8  grams  of  nitrogen,  or 
392  grams  of  proteid,  and  this  without  adding  very  largely 
to  the  intake  of  non-nitrogenous  matter.  This  experiment 
affords  a  striking  illustration  of  the  ability  of  the  body  to 
"fatten  on  nitrogen,"  but  it  is  very  doubtful  if  such  results 
can  generally  be  obtained.  Lu'thje,1  however,  has  reported  a 
large  retention  of  nitrogen  on  a  diet  containing  50  grams  of 
nitrogen  daily,  with  a  fuel  value  of  4000  calories.  It  is 
more  than  probable  that  there  existed  in  these  particular 
cases  some  personal  peculiarity  or  idiosyncrasy  which  favored 
the  proteid-sparing  power.  The  personal  coefficient  of  nutri- 
tion is  not  to  be  ignored;  it  shows  itself  in  many  ways,  and 
the  above  results  are  to  be  counted  among  those  that  are  ex- 
ceptional and  not  the  rule.  In  the  words  of  Magnus-Levy, 
"  a  given  diet  with  Cassius  may  lead  to  different  results  than 
with  Anthony." 

For  the  study  of  many  questions  in  nutrition,  it  becomes 
necessary  to  determine  accurately  the  transformations  of 
energy  within  the  body  as  contrasted  with  the  transformation 
of  matter;  the  total  income  and  outgo  of  energy,  measured 
in  terms  of  heat,  are  to  be  compared  one  with  the  other  and 
a  balance  struck.  Further,  in  studying  the  metabolism  of 
carbohydrate  and  fat  it  is  necessary  to  determine  the  output 
of  gaseous  products  through  the  lungs  and  skin ;  to  estimate 
the  excretion  of  carbon  dioxide  and  water,  and  the  intake  of 
oxygen.  For  these  purposes,  a  special  form  of  apparatus 
known  as  a  respiration  calorimeter  is  employed.  The  double 

1  Zeitschrift  fur  klinische  Medizin,  Band  44,  p.  22. 


102  THE  NUTRITION  OF  MAN 

name  is  indicative  of  the  twofold  character  of  the  apparatus, 
viz.,  a  suitably  constructed  chamber  so  arranged  as  to  permit 
of  measuring  at  the  same  time  the  respiratory  products  and  the 
energy  given  off  from  the  body.  The  form  of  apparatus  best 
known  to-day,  and  with  which  exceedingly  satisfactory  work 
has  been  done,  is  the  Atwater-Rosa  apparatus,  as  modified  by 
Benedict.  It  consists  essentially  of  a  respiration  chamber,  in 
reality  an  air-tight,  constant-temperature  room  (with  walls 
of  sheet  metal,  outside  of  which  are  two  concentric  coverings 
of  wood  completely  surrounding  it,  with  generous  air  spaces 
between),  sufficiently  large  to  admit  of  a  man  living  in  it  for 
a  week  or  more  at  a  time.  Connected  with  the  chamber  is 
a  great  variety  of  complex  apparatus  for  maintaining  and 
analyzing  the  supply  of  oxygen,  determining  the  amount  of 
carbon  dioxide  and  of  water,  etc.,  etc.  As  an  apparatus  for 
measuring  heat,  the  chamber  may  be  described  as  "  a  constant- 
temperature,  continuous-flow  water  calorimeter,  so  devised 
and  manipulated  that  gain  or  loss  of  heat  through  the  walls 
of  the  chamber  is  prevented,  and  the  heat  generated  within 
the  chamber  cannot  escape  in  any  other  way  than  that  pro- 
vided for  carrying  it  away  and  measuring  it."  1 

In  illustration  of  the  efficiency  of  an  apparatus  of  this  de- 
scription, and  of  the  close  agreement  obtainable  by  direct  calori- 
metric  measurement  with  the  estimated  energy,  as  figured  from 
the  materials  oxidized  in  the  body,  we  may  quote  the  following 
data  from  Dr.  Benedict's  report,  referred  to  in  the  footnote. 
The  subject  was  a  young  man  who  had  been  fasting  for  five 
days.  The  experiment  deals  with  the  metabolism  on  the  first 
day  after  the  fast,  when  a  diet  composed  mainly  of  milk  was 


1  For  an  account  of  the  respiration  calorimeter  and  the  great  diversity  of  ap- 
paratus accessory  thereto,  together  with  a  description  of  the  methods  of  measure- 
ment, analysis,  etc.,  see  Publication  No.  42,  Carnegie  Institution  of  Washington, 
"  A  Respiration  Calorimeter  with  Appliances  for  the  Direct  Determination  of 
Oxygen."  By  W.  O.  Atwater  and  F.  G.  Benedict. 


THE   BALANCE   OF  NUTRITION 


103 


made  use  of,  containing  53.31  grams  of  proteid,  211.87  grams 
of  fat,  and  75.41  grams  of  carbohydrate.  The  following  table 
shows  the  results  of  the  experiment: 


Heat  of  Combustion  of 
Food  and  Excreta  as 
Determined  by  Bomb 
Calorimeter. 

Avail- 
able 
Energy 

Total 
Energy 
from  Body 

(f) 

Estimated 
Energy 
from 
Material 

Heat 
Measured 
by 
Respira- 

Heat Measured 
Greater  or  Less 
than  Estimated. 

K&. 

Excre- 
ment. 

Urine. 

Food. 
a-(b+c) 

Gained  or 
Lost.1 

in  the 
Body, 
d  —  e. 

tion  Cal- 
orimeter. 

Amount. 

Propor- 
tion. 

calories 

calories 

calories 

calories 

calories 

calories 

calories 

calories 

per  cent 

2569 

149 

103 

2317 

+229 

2088 

2113 

+25 

+1.2 

As  is  seen  from  the  above  figures,  the  total  fuel  value  of 
the  food  was  2569  calories.  The  fuel  value  of  the  unoxidized 
portion  of  the  food  contained  in  the  excreta  was  149  +  103 
calories,  leaving  as  the  available  energy  of  the  food  2317 
calories.  This  must  be  farther  corrected  by  the  fact,  men- 
tioned in  the  footnote,  that  a  portion  of  the  food  was  stored 
as  fat  and  glycogen,  while  the  body  lost  at  the  same  time  a 
small  amount  of  proteid.  Making  the  necessary  correction 
for  these  causes,  we  find  2088  calories  as  the  energy  from 
material  oxidized  in  the  body.  The  actual  output  of  energy 
as  measured  by  the  calorimeter  was  2113  calories,  only  1.2 
per  cent  greater  than  the  estimated  amount. 

By  aid  of  the  respiration  calorimeter,  many  important  ques- 
tions in  nutrition  can  be  more  or  less  accurately  answered, 
especially  such  as  relate  to  the  total  energy  requirements  of 
the  body.  The  law  of  the  conservation  of  energy  obtains  in 
the  human  body  as  elsewhere,  and  if  we  can  measure  with 
accuracy  the  total  heat  output,  with  any  energy  liberated  in 
the  form  of  work,  and  at  the  same  time  determine  the  total 
excretion  of  carbon  dioxide,  water,  nitrogen,  etc.,  together 


1  In  the  experiment,  the  body  lost  29.16  grams  of  proteid  =  165  calories,  but 
gained  fat  and  glycogen  =  393  calories.  Hence,  there  were  229  calories  gained 
from  body  material. 


104  THE  NUTRITION  OF  MAN 

with  the  intake  of  oxygen,  it  becomes  not  only  possible  to 
ascertain  the  energy  requirements  of  the  body  under  different 
conditions,  but,  aided  by  data  obtainable  through  study  of  the 
exchange  of  matter,  we  can  draw  important  conclusions  con- 
cerning the  sources  of  the  energy,  i.  e.,  whether  from  protcid, 
fat,  or  carbohydrate. 

It  is  obvious  that  a  man  asleep,  or  lying  quietly  at  rest,  in 
the  calorimeter,  especially  when  he  has  been  without  food  for 
some  hours,  furnishes  suitable  conditions  for  ascertaining  the 
minimal  energy  requirements  of  the  body.  Under  such  con- 
ditions, bodily  activity  and  heat  output  are  at  their  lowest, 
and  we  are  thus  afforded  the  means  of  determining  what  is 
frequently  called  the  basal  energy  exchange  of  the  body. 
The  following  table  taken  from  Magnus-Levy,  and  embody- 
ing results  from  many  sources,  shows  the  heat  production 
during  sleep,  calculated  for  24  hours,  of  various  individuals  of 
different  body-weight  and  of  different  body  surface. 

I  venture  to  present  these  individual  results,  rather  than 
make  a  general  statement  simply,  because  it  is  important  to 
recognize  the  fact  that  the  basal  energy  exchange  differs  ac- 
cording to  body-weight,  extent  of  body  surface,  and  the  con- 
dition of  the  body.  In  the  table,  the  results  are  arranged  in 
the  order  of  body- weight,  and  it  is  plain  to  see  that  the  abso- 
lute energy  exchange  is  greater  with  heavy  persons  than  with 
light,  yet  the  energy  exchange  does  not  increase  in  propor- 
tion to  increase  of  body- weight.  With  a  man  of  83  kilos 
body- weight,  the  basal  exchange  is  only  30-40  per  cent 
higher  than  in  a  man  of  43  kilos  body- weight.  In  other 
words,  the  man  of  small  body-weight  has,  per  kilo,  a  much 
higher  basal  exchange  than  the  heavier  man.  The  energy 
exchange  is  more  closely  proportional  to  the  extent  of  body 
surface  than  to  weight. 

As  Richet  has  expressed  it,  the  basal  energy  exchange  is 
inversely  proportional  to  the  body- weight  and  directly  propor- 


THE   BALANCE   OF  NUTRITION 


105 


Body-weight 
of  the 
Individual. 

Total  Calories 
for  24  Hours. 

Calories  per 
Kilo  of 
Body-weight. 

Body-weight 
of  the 
Individual. 

Total  Calories 
for  24  Hours. 

Calories  per 
Kilo  of 
Body-weight. 

kilos 

kilos 

43.2 

1333 

30.9 

67.6 

1608 

23.8 

48.0 

1214 

25.3 

67.5 

1621 

24.0 

50.0 

1315 

25.9 

70.0 

1661 

23.7 

53.0 

1527 

28.8 

70.0 

1620 

23.1 

55.0 

1590 

28.9 

71.2 

1787 

25.1 

56.5 

1519 

26.8 

72.6 

1550 

21.3 

57.2 

1560 

27.3 

72.7 

1657 

22.8 

58.0 

1510 

26.0 

73.0 

1584 

21.7 

62.5 

1431 

22.9 

73.0 

1630 

22.4 

63.0 

1418 

22.5 

75.6 

1670 

22.1 

63.0 

1492 

23.7 

82.0 

1556 

19.0 

64.0 

1656? 

25.8 

82.7 

2030? 

24.5 

64.9 

1475 

22.7 

83.5 

1670 

20.0 

65.0 

1498 

23.0 

88.3 

2019? 

22.9 

65.0 

1445 

22.2 

90.4 

1773 

19.6 

tional  to  the  body  surface.  This  is  in  harmony  with  the  view 
advanced  by  v.  Hosslin,  "  that  all  the  important  physiological 
activities  of  the  body,  including  of  course  its  internal  work 
and  the  consequent  heat  production,  are  substantially  propor- 
tional to  the  two-thirds  power  of  its  volume,  and  that  since 
the  external  surface  bears  the  same  ratio  to  the  volume,  a  pro- 
portionality necessarily  exists  between  heat  production  and 
surface."1 

There  are,  however,  many  circumstances  that  modify,  or 
influence,  energy  exchange.  Thus,  the  taking  of  food,  with 
all  the  attendant  processes  of  digestion,  assimilation,  etc.,  in- 

i  See  Armsby :  Principles  of  Animal  Nutrition,  p.  368. 


106 


THE  NUTRITION   OF  MAN 


volves  an  expenditure  of  energy  not  inconsiderable.  This 
has  been  experimentally  demonstrated  on  man  by  several  in- 
vestigators. With  fatty  food,  Magnus-Levy  found  that  his 
subject  lying  upon  a  couch,  as  completely  at  rest  as  possible, 
produced  in  the  24  hours  1547  calories  when  94  grams  of  fat 
were  eaten,  and  1582  calories  when  195  grams  of  fat  were 
consumed.  The  increase  of  heat  production  over  the  basal 
energy  exchange  was  10  and  58  calories  respectively.  With 
a  mixed  diet,  where  proteid  food  is  a  conspicuous  element,  the 
increase  in  heat  production  is  much  more  marked.  Thus,  in 
some  experiments  reported  from  Sweden  the  following  data 
were  obtained : * 


Day. 

Energy  of  the  Food. 

Heat  Production. 

First 

calories 
4141 

calories 

Second 

4277 

2705 

Third 

0 

2220 

Fourth 

0 

2102 

Fifth 

0 

2024 

Sixth 

0 

1992 

Seventh 

0 

1970 

Eighth 

4355 

2436 

Ninth 

3946 

2410 

We  see  here  an  increase  of  495  calories  per  day  in  heat  pro- 
duction, due  to  metabolism  of  the  food  ingested.  In  other 
words,  with  a  basal  energy  exchange  of  2022  calories,  the 
average  of  the  five  fasting  days,  energy  equivalent  to  495 
calories  was  expended  in  taking  care  of  the  ingested  food. 
It  should  be  added,  however,  that  the  daily  ration  here  was 


1  Taken  from  Armsby  :  Principles  of  Animal  Nutrition,  p.  383. 


THE  BALANCE  OF  NUTRITION  107 

somewhat  excessive,  4193  calories  being  considerably  in  ex- 
cess of  the  requirements  of  the  body.  Finally,  it  should  be 
stated  that  of  the  several  classes  of  foods,  proteids  cause  the 
greatest  increase  in  metabolism  and  fats  the  least. 

In  studying  heat  production  in  the  body  under  varying 
conditions,  one  of  the  important  aids  in  drawing  conclusions 
as  to  the  character  of  the  body  material  burned  up  is  the 
respiratory  quotient.  This  is  the  relationship,  or  ratio,  of 
the  oxygen  absorbed  to  the  oxygen  of  the  carbon  dioxide 

CO 

eliminated,  viz.,  ~^~  •  Carbohydrates  (C6H12  O6,  C12H22On) 

U2 

all  contain  hydrogen  and  oxygen  in  the  proportion  to  form 
water,  H2O,  and  in  their  oxidation  they  need  of  oxygen  only 
such  quantity  as  will  suffice  to  oxidize  the  carbon  (C)  of  the 
sugar  to  carbon  dioxide  (CO2).  Carbohydrates,  starch  and 
sugars,  have  a  respiratory  quotient  of  1.00.  Fat,  on  the 
other  hand,  has  a  respiratory  quotient  of  0.7,  and  proteid,  0.8. 
Hence,  it  is  easy  to  see  that  the  respiratory  quotient  will 
approach  nearer  to  unity  as  the  quantity  of  carbohydrate 
burned  in  the  body  is  increased.  Similarly,  the  respiratory 
quotient  will  grow  smaller  the  larger  the  amount  of  fat 
burned  up.  Practically,  we  never  find  a  respiratory  quotient 
of  1.0  or  0.7,  because  there  is  always  some  oxidation  of  pro- 
teid in  the  body.  If,  by  way  of  illustration,  we  assume  that 
the  energy  of  the  body  under  given  conditions  comes  from 
proteid  to  the  extent  of  15  per  cent,  while  the  remaining  85 
per  cent  is  derived  from  the  oxidation  of  carbohydrate,  the 
respiratory  quotient  will  be  0.971.  If,  however,  the  85  per 
cent  of  energy  comes  from  fat,  the  respiratory  quotient  will 
change  to  0.722.  In  the  resting  body,  as  in  the  e  rly  morn- 
ing hours,  after  a  night's  sleep  and  before  food  is  taken,  the 
respiratory  quotient  is  generally  in  the  neighborhood  of  0.8. 
When,  however,  as  sometimes  happens,  the  quotient  at  this 
time  of  day  approaches  0.9,  it  must  be  assumed  that  sugar  is 


108  THE  NUTRITION  OF  MAN 

being  burned  in  the  body,  presumably  from  carbohydrate  still 
circulating  from  the  previous  day's  intake. 

As  can  easily  be  seen,  any  special  drain  upon  either  fat  or 
carbohydrate  in  the  processes  of  the  body  will  be  indicated  at 
once  by  a  corresponding  change  in  the  respiratory  quotient. 
This  we  shall  have  occasion  to  notice  later  on,  in  considering 
the  source  of  the  energy  of  muscle  contraction.  Further,  the 
respiratory  quotient  will  naturally  change  in  harmony  with 
transformations  in  the  body  which  involve  alterations  in 
oxygen -con  tent,  without  the  oxygen  of  the  inspired  air  being 
necessarily  involved ;  as  in  the  formation  of  a  substance  poor 
in  oxygen,  such  as  fat,  from  a  substance  rich  in  oxygen,  such 
as  carbohydrate.  Moreover,  the  reversal  of  this  reaction,  as  in 
the  formation  of  sugar  from  proteid  with  a  taking  on  of  oxy- 
gen, will  produce  a  corresponding  effect  upon  the  respiratory 
quotient.  As  Magnus-Levy  has  clearly  pointed  out,  in  the 
formation  of  fat  from  carbohydrate,  carbon  dioxide  is  pro- 
duced in  large  amount  without  the  oxygen  of  the  inspired  air 
being  involved  at  all.  In  such  a  change,  100  grams  of  starch 
will  yield  about  42  grams  of  fat,  while  at  the  same  time  45 
grams  of  carbon  dioxide  will  be  produced.  This  might  cause 
the  respiratory  quotient  to  rise  as  high  as  1.38.  Again,  in 
the  formation  of  sugar  from  proteid,  the  respiratory  quotient 
may  sink  very  decidedly,  the  changes  involved  being  accom- 
panied by  a  taking  on  of  oxygen  from,  the  air,  without, 
however,  any  corresponding  increase  of  carbon  dioxide 
in  the  expired  air.  Assuming  a  manufacture  of  60  grams 
of  dextrose  from  100  grams  of  proteid,  i.  e.,  from  the  non- 
nitrogenous  moiety  of  the  proteid  molecule,  a  respiratory  quo- 
tient of  0.613  would  be  possible.  Thus,  a  diabetic  patient, 
living  upon  a  carbohydrate-free  diet,  consuming  only  proteid 
and  fat,  may  show  a  respiratory  quotient  of  0.613-0.707. 
These  illustrations  will  suffice  to  show  how  chemical  altera- 
tions taking  place  in  the  body,  involving  transformations  of 


THE  BALANCE  OF  NUTKITION  109 

proteid,  fat,  and  carbohydrate  of  the  tissues  and  of  the  food, 
may  produce  alterations  in  the  respiratory  quotient  without 
necessarily  being  directly  connected  with  intake  of  oxygen  or 
output  of  carbon  dioxide  through  the  lungs ;  and  how,  con- 
versely, the  respiratory  quotient  becomes  a  factor  of  great 
significance  in  throwing  light  upon  the  character  of  the 
nutritive  changes  taking  place  in  the  body. 

Among  the  various  conditions  that  influence  the  energy 
exchange  of  the  body,  muscle  work  stands  out  as  the  most 
conspicuous.  It  needs  no  argument  to  convince  one  that  all 
forms  of  muscular  activity  involve  liberation  of  the  energy 
stored  up  in  the  tissues  of  the  body ;  and  consequently  that 
all  work  accomplished  means  chemical  decomposition,  in 
which  complex  molecules  are  broken  down  into  simple  ones 
with  liberation  of  the  contained  energy,  the  energy  exchange 
being  proportional  to  the  amount  of  work  done.  As  we  have 
seen,  the  basal  energy  exchange  of  the  normal  individual  is 
ascertained  by  studying  his  heat  production  while  at  rest  — 
best  during  sleep  —  without  food,  when  involuntary  muscle 
activity  and  heat  production  are  at  their  lowest.  The 
maximum  energy  exchange  is  seen  in  the  individual  at  hard 
muscular  work.  Heat  production  is  then  at  its  highest,  as 
can  be  ascertained  by  direct  calorimetric  observation ;  or,  by 
studying  the  output  of  excretory  products,  which  measure 
the  extent  of  the  oxidative  processes  from  which  comes  the 
energy  for  the  accomplishment  of  the  work.  As  an  illustra- 
tion of  the  general  effect  of  muscular  work  on  the  energy  ex- 
change of  the  body,  we  may  cite  a  summary  of  some  results 
reported  by  Atwater  and  Benedict,1  the  figures  given  being 
average  results,  from  several  individuals,  and  covering  differ- 
ent periods  of  time.  Though  not  strictly  comparable  in  all 
details,  they  are  sufficiently  so  to  illustrate  the  main  principle. 

1  Atwater  and  Benedict :  Experiments  on  the  Metabolism  of  Matter  and 
Energy  in  the  Human  Body  1900-1902.  Bulletin  No.  136,  Office  of  Experi- 
ment Stations,  U.  S.  Department  of  Agriculture,  1903,  p.  141. 


110 


THE  NUTRITION  OF  MAN 


HEAT  GIVEN  OFF  BY  BODY,  INCLUDING  FOR   WORK 

EXPERIMENTS   THE   HEAT  EQUIVALENT  OF 

THE  EXTERNAL  MUSCULAR   WORK. 


Rates  per  Hour. 

Kind  of  Experiment. 

Amount 
of  Heat 
in  24 

Day  Periods. 

Night  Periods. 

Average 
for 
24  Hours. 

Hours. 

7  A.  M.  to 

1  P.  M.  tO 

7  P.  M.  tO 

1  A.  M.  tO 

IP.  M. 

7  P.M. 

1  A.M. 

7A.M. 

calories 

calories 

calories 

calories 

calories 

calories 

Rest  experiments 

2262 

106.3 

104.4 

98.3 

67.9 

94.3 

Work  experiments 
Heat  eliminated 

[4226 

231.7 

236.6 

118.1 

78.4 

166.6 

Heat  equivalent  of 
external  muscu- 

>  451 

68.6 

56.8 

lar  work 

> 

Total    .    .    . 

4676 

290.2 

292.4 

118.1 

78.4 

194.8 

The  work  done  in  these  experiments  was  on  a  stationary 
bicycle  in  the  calorimeter,  and  the  heat  equivalent  was  cal- 
culated from  measurements  made  by  an  ergometer  attached 
to  the  bicycle.  We  are  not  concerned  here  with  details,  but 
simply  with  the  general  question  of  the  influence  of  muscular 
work  upon  the  energy  exchange  of  the  body.  We  note  that 
the  work  of  the  day  periods,  7  A.  M.  to  7  P.  M.,  resulted,  in 
the  several  cases  brought  together  under  the  average  figures, 
in  an  increased  heat  production  amounting  to  more  than  100 
per  cent.  Further,  we  observe  that  in  the  body,  as  in  all 
machines,  only  a  fraction  of  the  energy  liberated  by  the 
accelerated  chemical  decomposition,  or  oxidation,  was  mani- 
fested as  mechancial  work,  the  larger  part  by  far  being  heat 
eliminated  and  lost.  Thus,  Zuntz  has  found  that,  in  man, 
about  35  per  cent  of  the  extra  energy  of  the  food  used  in 
connection  with  external  muscular  work  is  available  for  that 


THE  BALANCE   OF  NUTBITION 


111 


work.  This,  however,  shows  a  noticeably  higher  degree  of 
efficiency  than  is  generally  obtainable  by  the  best  steam  or 
oil  engines.  Lastly,  attention  may  be  called  to  the  fact  that 
after  the  work  of  the  day  was  finished  at  7  P.  M. ,  the  next 
period  of  six  hours  still  showed  an  accelerated  metabolism,  as 
contrasted  with  what  took  place  during  absolute  rest. 

As  bearing  upon  the  exchange  of  matter  in  the  body  in  con- 
nection with  muscular  work,  and  as  showing  the  relationship 
which  exists  here  between  energy  exchange  and  exchange  of 
matter,  we  may  quote  a  few  data  relating  to  the  elimination 
of  carbon  dioxide;  remembering  that  this  substance  repre- 
sents particularly  the  final  oxidation  product  in  the  body  of 
carbonaceous  materials,  such  as  fat  and  carbohydrate.  The 
following  data,  taken  from  Atwater  and  Benedict,1  being 
results  of  experiments  upon  the  subject  "  J.  C.  W.,"  are  of 
valuers  showing  the  variations  in  output  of  carbon  dioxide 
that  may  be  expected  under  the  conditions  described : 


Period. 

Rest  Ex- 
periments 
without 
Food. 

Rest  Ex- 
periments 
with  Food. 

Work  Ex- 
periments 
with  Carbo- 
hydrate 
Diet 

Work  Ex- 
periments 
with 
Fat  Diet. 

Extra 
Severe 
Work 
Experiment 
with 
Fat  Diet. 

7  A.  M.  to  1  P.  M. 

grams 

189.6 

grams 
230.4 

grams 

694.0 

grams 
642.3 

grams 
907.0 

1  P.  M.  tO  7  P.  M. 

172.6 

232.0 

705.6 

634.8 

821.3 

7  P.  M.  tO  1  A.  M. 

167.2 

196.6 

260.1 

230.3 

842.7 

1  A.M.  tO  7  A.M. 

146.7 

153.1 

161.1 

157.6 

502.6 

Total  for  24  hours 

676.1 

812.1 

1820.8 

1665.0 

3073.6 

In  considering  these  figures  bearing  on  the  output  of  car- 
bon dioxide  under  the  conditions  specified,  we  note  at  once 
a  correspondence  with  the  total  energy  exchange,  as  indicated 


Loc,  cit,  pp.  130  and  131. 


112  THE  NUTRITION  OF  MAN 

in  the  preceding  table.  As  previously  stated,  we  are  at 
present  dealing  simply  with  generalities,  and  the  important 
point  to  be  observed  here  is  that  muscular  work  —  7  A.  M. 
to  7  P.  M.  —  in  the  work  experiments,  increases  enormously 
the  output  of  carbon  dioxide.  We  see  clearly  emphasized 
a  connection  between  the  total  energy  exchange  of  the  body, 
as  expressed  in  calories  or  heat  units,  and  the  oxidation  of 
carbonaceous  material,  of  which  carbon  dioxide  is  the  natural 
oxidation  product.  We  note  that  on  the  cessation  of  work 
—  7  P.  M.  to  7  A.  M.  —  the  output  of  carbon  dioxide  tends 
to  drop  back  to  the  level  characteristic  of  the  corresponding 
period  in  rest,  with  or  without  food.  In  the  experiment 
with  "extra  severe  muscular  work,"  the  results  are  different 
simply  because  here  the  subject  worked  sixteen  hours, 
necessitating  a  portion  of  the  work  being  done  at  night-time. 
Finally,  it  should  be  mentioned  that  the  differences  in  out- 
put of  carbon  dioxide  in  these  experiments  are  somewhat 
greater  than  in  many  experiments  of  this  type,  although  all 
show  the  same  general  characteristics.  This  may  be  ex- 
plained, as  stated  by  the  authors  from  whom  the  data  are 
taken,  "  by  the  fact  that  J.  C.  W.  was  a  larger  and  heavier 
man  than  any  of  the  others ;  that  the  differences  in  diet  were 
wider,  and  that  the  amounts  of  external  muscular  work  were 
larger  in  these  experiments  than  in  those  with  the  other 
subjects." 

If  we  pass  from  experiments  of  this  type,  conducted  in 
a  calorimeter,  to  those  cases  where  competitive  trials  of  en- 
durance are  held  by  trained  athletes,  i.  e.,  where  external 
muscular  activity  is  pushed  to  the  extreme  limit,  we  then  see 
even  more  strikingly  displayed  the  effect  of  work  in  increas- 
ing the  energy  exchange  of  the  body.  One  of  the  best  illus- 
trations of  this  type  of  experiment  is  to  be  found  in  the  ob- 
servations made  in  connection  with  the  six-day  bicycle  race 
held  in  New  York  City,  at  the  Madison  Square  Garden,  in 


THE  BALANCE   OF  NUTRITION 


113 


December,  1898. l  The  observations  in  question  were  made 
upon  three  of  the  athletes,  one  of  whom  withdrew  early  in 
the  fourth  day,  while  the  others  continued  until  the  close  of 
the  race  — 142  consecutive  hours  —  winning  the  first  and 
fourth  places,  respectively.  The  following  table  gives  the 
computation  of  energy  of  the  material  metabolized,  exclusive 
of  body-fat  lost: 


Subject. 

Duration  of 
Experiment. 

Total  Energy 
Metabolized. 

Average  per 
Day. 

Miller  

days 

6 

calories 
28917 

calories 
4820 

Albert  

6 

36441 

6074 

Pilkington     .... 

3 

13301 

4464 

Miller,  the  winner  of  the  race,  who  averaged  a  daily  energy 
exchange  of  4820  calories,  rode  2007  miles  during  the  week, 
and  finished  the  race  without  physical  or  mental  weakness 
resulting  from  the  fatigue  and  strain.  During  the  first  five 
days,  he  rode  about  21  hours  a  day  and  slept  only  1  hour. 
Albert,  who*  weighed  a  few  pounds  less  than  Miller,  covered 
1822  miles  in  109  hours,  with  an  average  daily  exchange  of 
6074  calories.  We  may  add  a  table  (on  the  following  page) 
showing  the  balance  of  income  and  outgo  of  nitrogen  in  these 
three  subjects,  as  being  of  general  interest  in  this  connection. 
The  figures  given  are  averages  per  day. 

The  special  significance  of  these  data,  as  bearing  upon 
the  topic  under  discussion,  is  that  apparently  all  three  of  the 
subjects  were  drawing  in  a  measure  upon  their  body  material. 
As  stated  by  Atwater  and  Sherman,  Pilkington  lost  per  day 
5. 1  grams  of  nitrogen ;  that  is  to  say,  the  total  nitrogen  ex- 


i  See  W.  O.  Atwater  and  II.  C.  Sherman :  The  effect  of  severe  and  prolonged 
muscular  work  on  food  consumption,  digestion,  and  metabolism.  Bulletin  No. 
98,  Office  of  Experiment  Stations,  U.  S.  Department  of  Agriculture. 

8 


114 


THE  NUTRITION  OF  MAN 


Dura- 
tion 

Income  in  Food. 

Nitrogen. 

Subject. 

of 

Exp. 

Pro- 
teid. 

Fat. 

Carbo- 
hydrate. 

Fuel 
Value. 

In 
Food. 

In 
Urine. 

In 

Excre- 
ment. 

Loss. 

days 

grams 

grams 

grams 

calories 

grams 

grams 

grams 

grams 

Miller     .    . 

6 

169 

181 

585 

4770 

29.4 

36.2 

1.8 

8.6 

Albert    .    . 

6 

179 

198 

559 

6095 

29.1 

33.7 

2.5 

7.1 

Pilkington 

3 

211 

178 

609 

4610 

36.0 

38.9 

2.2 

5.1 

ere  ted  exceeded  the  total  nitrogen  of  the  food  by  5.1  grams 
per  day,  corresponding  to  33  grams  of  proteid,  which  must 
have  been  drawn  from  the  supply  in  the  body.  If  we  assume 
that  lean  flesh  contains  25  per  cent  of  proteid,  this  would 
mean  about  4j  ounces  per  day.  The  other  two  subjects, 
Miller  and  Albert,  lost  from  the  body  per  day  8. 6  grams  and 
7.1  grams  respectively  of  nitrogen,  which  would  imply  a  loss 
of  about  54  grams  and  44  grams  of  body  proteid  respectively, 
or  8  ounces  and  6J  ounces  of  lean  flesh  per  day.  It  is  evi- 
dent, therefore,  that  none  of  the  three  subjects  consumed 
sufficient  food  to  avoid  loss  of  body  proteid,  under  the  exist- 
ing conditions  of  muscular  activity.  Indeed,  it  may  be  noted 
in  Miller's  case  that  the  average  fuel  value  of  the  food  per 
day  was  4770  calories,  while  the  average  expenditure  of 
energy  per  day  was  4820  calories.  We  should  naturally 
expect,  however,  that  any  small  deficiency  in  fuel  value 
would  be  made  good  by  a  call  upon  body  fat.  "Why  the 
body  should  use  its  own  substance  under  such  circumstances 
is  a  question  which  at  present  cannot  be  satisfactorily  an- 
swered. .The  fact  that  such  was  the  case,  each  of  the  con- 
testants who  finished  the  race  consuming  during  the  period 
body  protein  equivalent  to  2  or  3  pounds  of  lean  flesh,  and 
that  no  injury  resulted  therefrom,  would  seem  to  indicate 
that  these  men  had  stores  of  protein  which  could  be  metabo- 


THE  BALANCE  OF  NUTBITION  115 

lized  to  aid  in  meeting  the  demands  put  upon  the  body  by 
the  severe  exertion,  without  robbing  any  of  the  working 
parts,  and  at  the  same  time  relieving  the  system  of  a  part  of 
the  labor  of  digestion.  Possibly,  the  ability  to  carry  such 
a  store  of  available  protein  is  one  of  the  factors  which  make 
for  physical  endurance."1  This  possibility  we  shall  have 
occasion  to  discuss  in  another  connection.  At  present,  the 
facts  presented  are  to  be  accepted  as  accentuating  the  general 
law  that  the  energy  exchange  of  the  body,  everything  else 
being  equal,  is  increased  proportionally  to  increase  in  the 
extent  of  external  muscular  activity.  It  may  be  noted  that 
Albert,  who  did  considerably  less  work  than  Miller,  showed 
a  much  larger  exchange  of  energy  than  the  latter  athlete. 
This,  however,  is  to  be  connected  with  the  fact  that  his  fuel 
intake  was  1300  calories  larger  per  day  than  Miller's;  in  other 
words,  the  conditions  were  not  equal.  This  fact  also  calls  to 
mind  the  observations  of  Schnyder,2  who,  studying  the  rela- 
tionship between  muscular  activity  and  the  production  of 
carbon  dioxide,  maintained  that  the  quantity  of  this  excretory 
product  formed  depends  less  upon  the  amount  of  work  accom- 
plished than  upon  the  intensity  of  the  exertion ;  efficiency  in 
muscular  work  varying  greatly  with  the  condition  of  the  sub- 
ject, and  his  familiarity  with  the  particular  task  involved. 

From  what  has  been  said,  it  is  obvious  that  oxygen  con- 
sumption, as  well  as  output  of  carbon  dioxide,  must  vary 
enormously  with  variations  in  the  muscular  activity  of  the 
body.  The  one  important  factor  influencing  the  quantities 
of  oxygen  and  carbon  dioxide  exchanged  in  the  lungs,  i.  «., 
the  extent  of  the  respiratory  interchange,  is  muscular  activity ; 
and  since,  as  we  have  seen,  carbonaceous  material  is  the  sub- 
stance mainly  oxidized  in  muscle  work,  it  follows,  as  carbon 


1  Atwater  and  Sherman.     Loc.  cit.,  p  61. 

2  L.  Schnyder:    Muskelkraft   und   Gaswechsel.     Zeitschrift  fiir  Biologie, 
Band  33,  p.  289. 


116 


THE  NUTRITION  OF  MAN 


dioxide  is  excreted  principally  through  the  lungs,  that  the 
respiratory  interchange  becomes  in  good  measure  an  indicator 
of  the  extent  of  chemical  decomposition  incidental  to  external 
work.  If  we  recall  that  man,  on  an  average,  at  each  inspira- 
tion draws  in  about  500  cubic  centimeters  of  air  (30  cubic 
inches),  and  that  for  the  24  hours  he  averages  15  breaths  a 
minute,  it  is  easy  to  see  that  in  one  minute  the  average  man 
will  inspire  7.5  litres  of  air,  or  450  litres  an  hour,  with  a 
total  of  10,800  litres  for  the  entire  day,  which  is  equivalent 
to  about  380  cubic  feet.  This  would  be  a  volume  of  air  just 
filling  a  room  7£  feet  in  length,  width,  and  height.  Inspired 
air  loses  to  the  body  4.78  volumes  per  cent  of  oxygen,  while 
expired  air  contains  an  excess  of  4.34  volumes  per  cent  of 
carbon  dioxide.  In  muscular  work,  respiration  is  increased 
in  frequency  and  in  depth.  The  volume  of  air  exchanged 
in  the  lungs  during  severe  labor  may  be  increased  sevenfold, 
while  oxygen  consumption  and  carbon  dioxide  excretion  are 
frequently  increased  7-10  times.  The  following  figures, 
being  values  for  one  minute,  show  the  effect  on  oxygen  con- 
sumption of  walking  on  a  level  and  climbing,  the  subject 
being  a  man  of  55.5  kilos  body-weight:1 


Form  of  Work. 

Oxygen  Consumption  in  Cubic  Centimeters. 

Respiratory 
Quotient. 

Total. 

After  Deducting  Value 
for  Rest. 

Total. 

For  Each 
Kilo  of  Mov- 
ing Weight. 

Standing  at  rest    .    .    . 
Walking  on  a  level    .    . 
Climbing  .         .         .    . 

263.75 
763.00 
1253.20 

499.25 
989.45 

8.990 

17.819 

0.801 
0.805 
0.801 

1  G.  Katzenstein:  Ueber  die  Einwirkung  der  Muskelthatigkeit  auf  den 
Stoffverbraueh  des  Menschen.  Ffliiger's  Archiv  fur  die  gesanuute  Physiologie, 
Band  49,  p.  330.  Also  Magnus-Levy :  v.  Noordeu's  Handbuch  der  Pathologic 
der  Stoffwechsel,  p.  233. 


THE  BALANCE   OF  NUTBITIOtf  117 

Remembering  that  these  figures  represent  the  oxygen  con- 
sumption for  only  one  minute  of  time,  it  is  easy  to  see  the 
striking  effect  of  moderate  and  vigorous  exercise  on  respira- 
tory interchange.  Simply  walking  along  a  level  suffices  to 
increase  the  consumption  of  oxygen  threefold  over  what 
occurs  when  the  body  stands  at  rest.  When  the  more  vigor- 
ous exercise  attendant  on  lifting  the  body  up  a  steep  incline 
is  attempted,  most  striking  is  the  great  increase  in  the 
amount  of  oxygen  consumed.  We  thus  see  another  forcible 
illustration  of  the  influence  of  muscular  activity  upon  the 
exchange  of  matter  in  the  body,  and  a  further  confirmation 
of  the  statement,  so  many  times  made,  that  oxidation  —  es- 
pecially the  oxidation  of  fats  and  carbohydrates  by  which 
large  quantities  of  heat  are  set  free,  easily  convertible  into 
mechanical  energy  —  is  a  primary  factor  in  the  metabolic 
processes,  by  which  the  machinery  of  the  living  man  is  able 
to  work  so  efficiently. 

Finally,  we  cannot  avoid  the  conclusion  that  the  outgoings 
of  the  body,  in  the  form  of  matter  and  energy,  are  subject  to 
great  variation,  incidental  to  the  degree  of  activity  of  the 
day  or  hour.  The  ordinary  vicissitudes  of  life,  bringing 
days  of  physical  inaction,  followed  perhaps  by  periods  of 
unusual  activity;  changes  in  climatic  conditions,  with  their 
influence  upon  heat  production  in  the  body ;  alterations  in  the 
character  and  amount  of  the  daily  dietary,  etc.,  — all  seem- 
ingly combine  as  natural  obstacles  to  the  maintenance  of  a 
true  nutritive  balance.  Outgo,  however,  must  be  met  by 
adequate  amounts  of  proper  intake  if  there  is  to  be  an  ap- 
proach toward  a  balance  of  nutrition.  In  some  way  the 
normal,  healthy  man  does  maintain,  approximately  at  least, 
a  condition  of  balance ;  not  necessarily  for  every  hour  or  for 
every  day,  but  the  intake  and  outgo  if  measured  for  a  definite 
period,  not  too  short,  say  for  a  week  or  two,  will  be  found  to 
approach  each  other  very  closely.  Body  equilibrium  and 


118  THE  NUTRITION   OF   MAN 

approximate  nitrogen  balance  may  be  reasonably  looked  for, 
as  well  as  a  balance  of  total  energy,  in  the  case  of  a  healthy 
man  leading  a  life  which  conforms  to  ordinary  physiological 
requirements.  The  man  who,  on  the  other  hand,  consciously 
or  unconsciously,  continues  an  intake  way  beyond  the  outgo, 
whose  daily  income  of  nitrogen  and  total  fuel  value  far  ex- 
ceeds the  requirements  of  his  body,  obviously  lives  with  an 
accumulating  plus  balance,  which  ordinarily  shows  itself  in 
increasing  body-weight  and  with  a  storing  away  of  fat. 

Equally  conspicuous  is  the  effect  of  an  inadequate  income 
of  proper  nutriment;  a  food  supply  which  persistently  fails  to 
furnish  the  available  nitrogen  and  total  energy  value  called  for 
by  the  body  under  the  conditions  prevailing,  will  inevitably 
result  in  a  minus  balance,  which,  if  continued  too  long,  must 
of  necessity  tax  the  body's  store  to  the  danger  limit.  At  the 
same  time,  the  well-nourished  individual,  without  being  un- 
duly burdened  by  a  bulky  store  of  energy-containing  mate- 
rial, is  always  supplied  with  a  sufficient  surplus  to  meet  all 
rational  demands,  when  from  any  cause  the  intake  fails,  for 
brief  periods  of  time,  to  be  commensurate  with  the  needs  of  the 
body.  It  is  reasonable  to  believe,  however,  that  in  the  main- 
tenance of  good  health,  and  the  preservation  of  a  high  degree 
of  efficiency,  the  body  should  be  kept  in  a  condition  approach- 
ing a  true  nutritive  balance. 


CHAPTER  IV 

SOUKCE  OF  THE  ENEEGY  OF  MUSCLE  WORK,  WITH 
SOME  THEORIES   OF  PROTEID  METABOLISM 

TOPICS  :  Relation  of  muscle  work  to  energy  exchange.  Views  of 
Liebig.  Experimental  evidence.  Relation  of  nitrogen  excretion  to 
muscle  work.  Significance  of  the  respiratory  quotient  in  determin- 
ing nature  of  the  material  oxidized.  Fats  and  carbohydrates  as  source 
of  energy  by  muscles.  Utilization  of  proteid  as  a  source  of  energy. 
Formation  of  carbohydrate  from  proteid.  Significance  of  proteid 
metabolism.  Theories  of  Carl  Voit.  Morphotic  proteid.  Circulating 
proteid.  General  conception  of  proteid  metabolism  on  the  basis  of 
Voit's  theories.  Pfliiger's  views  of  proteid  metabolism.  Rapidity  of 
elimination  of  food  nitrogen.  Methods  by  which  nitrogen  is  split 
off  from  proteid.  Theories  of  Folin.  Significance  of  creatinin  and 
of  the  percentage  distribution  of  excreted  nitrogen.  Endogenous  or 
tissue  metabolism.  Exogenous  or  intermediate  metabolism.  Needs 
of  the  body  for  proteid  food  possibly  satisfied  by  quantity  sufficient  to 
meet  the  demands  of  tissue  or  endogenous  metabolism.  Bearings  of 
Folin 's  views  on  current  theories  and  general  facts  of  proteid  metabo- 
lism. Large  proteid  reserve  and  voluminous  exogenous  metabolism 
probably  not  needed.  Importance  of  feeding  experiments  in  determin- 
ing the  true  value  of  different  views. 

AS  we  have  already  seen,  every  form  of  muscular  activity 
begets  an  increase  in  the  energy  exchange  of  the  body. 
Between  the  two  extremes  of  absolute  rest  and  excessive 
muscular  exertion,  we  find  differences  of  2000  calories 
or  more  per  day  as  representing  the  degree  of  chemical  de- 
composition corresponding  to  the  particular  state  of  muscu- 
lar activity.  The  work  of  the  involuntary  muscles,  such  as 
have  to  do  with  peristalsis,  respiration,  rythmical  beat  of  the 
heart,  etc.,  is  a  relatively  constant  factor,  though  naturally 
subject  to  some  variation,  as  has  been  pointed  out  in  other 


120  THE  NUTRITION  OF  MAN 

connections.  External  muscular  activity,  however,  is  the  one 
factor  above  all  others  that  modifies  the  rate  of  energy  ex- 
change. A  little  longer  walk,  a  heavier  load  to  carry,  a  steeper 
hill  to  climb,  any  increase  great  or  small  in  the  activity  of 
the  muscles  of  the  body,  means  a  corresponding  increase  in 
chemical  decomposition,  with  increased  output  of  the  ordinary 
products  of  tissue  oxidation.  The  material  so  consumed,  or 
oxidized,  must  be  made  good  to  hold  the  body  in  equilibrium ; 
the  supplies  drawn  upon  are  to  be  replaced,  if  the  tissues  of 
the  body  are  to  be  kept  in  a  proper  state  of  efficiency. 

What  is  the  nature  of  the  material  used  up  in  connection 
with  muscle  work  ?  As  can  readily  be  seen,  this  is  an  important 
question,  for  on  its  answer  depends,  in  some  measure  at  least, 
the  character  of  the  proper  intake,  or  food,  to  be  supplied  in 
order  to  make  good  the  loss.  If  the  energy  of  mechanical 
work,  the  energy  of  muscle  contraction,  comes  from  the 
breaking  down  of  proteid  matter  alone,  then  obviously  exces- 
sive muscular  work  would  need  to  be  accompanied,  or  fol- 
lowed, by  a  generous  supply  of  proteid  food.  If,  on  the  other 
hand,  external  work  means  liberation  of  energy  solely  from 
non-nitrogenous  materials,  then  it  is  equally  clear  that  fats 
and  carbohydrates  are  the  proper  foods  to  offset  the  drain 
incidental  to  vigorous  muscular  action. 

The  views  of  Liebig,  briefly  referred  to  in  a  previous  chap- 
ter, held  sway  over  physiologists  for  many  years.  His 
dictum  that  proteid  foods  were  true  plastic  foods,  entering 
into  the  structure  of  the  tissues  of  the  body,  and  that  they 
alone  were  the  real  sources  of  muscular  energy,  met  for  a 
time  with  no  opposition.  It  was  not  until  the  advent  of 
a  more  critical  spirit,  accompanied  by  a  fuller  appreciation 
of  the  necessity  of  experimental  evidence,  that  physiologists 
began  to  test  with  scientific  accuracy  the  validity  of  the  cur- 
rent views.  It  is  worthy  of  note  that  long  prior  to  this  time, 
even  before  oxygen  was  discovered,  the  far-sighted  and  re- 


SOURCE   OF  ENERGY   OF   MUSCLE  WORK      121 

sourcef ul  John  Mayow,  in  his  work  with  the  various  "  spirits  " 
of  the  body  and  their  relation  to  respiration,  etc.,  evolved  the 
view  that  muscular  power  has  its  origin  in  the  combustion  of 
fat  brought  to  the  muscles  by  the  blood  and  burned  there  by 
aid  of  a  gas  or  "spirit"  taken  from  the  air  by  the  lungs,  and 
likewise  carried  to  the  muscles  by  the  circulating  blood.  Con- 
sidering the  time  when  Mayow  lived  and  the  dearth  of  true 
scientific  knowledge  as  we  measure  it  to-day,  his  hypothesis 
was  a  wonderful  forestalling  of  present  views. 

It  is  quite  obvious  that  the  views  of  Liebig,  if  true,  admit 
of  easy  proof;  since,  if  the  energy  of  muscular  power  comes 
from  the  breaking  down  of  proteid,  there  should  be  a  certain 
parallelism  between  the  output  of  nitrogen  from  the  body  and 
the  amount  of  muscular  work  accomplished,  everything  else 
being  equal.  As  stated  in  a  previous  chapter,  such  study  of 
this  question  as  was  made  soon  disclosed  the  fact  that  the  one 
element  above  all  others  that  seemed  to  influence  the  output 
of  nitrogen  was  the  intake  of  proteid  food.  Thus,  the  Eng- 
lish investigators,  Lawes  and  Gilbert,  found  by  experiment- 
ing with  animals  that  when  the  latter  were  kept  under 
uniform  conditions  of  muscular  work,  the  amount  of  nitro- 
gen excreted  ran  parallel  with  the  intake  of  nitrogen.  Fur- 
ther, in  the  early  experiments  of  Voit,  the  results  obtained 
clearly  showed  that  variations  in  the  amount  of  work  per- 
formed were  practically  without  influence  on  the  excretion 
of  nitrogenous  waste  products. 

The  experiment,  however,  that  came  as  a  death  blow  to 
the  theories  of  Liebig  was  that  of  Fick  and  Wislicenus,1 
who  in  1865  made  an  ascent  of  the  Faulhorn,  6500  feet 
high,  using  a  diet  wholly  non-nitrogenous.  From  the 
nitrogen  excreted  they  were  able,  of  course,  to  calculate 
the  amount  of  proteid  oxidized  in  the  body  during  the  period 

1  See  Gesammelte  Schriften  von  Adolf  Fick.  Ueber  die  Entstehung  der 
Muskelkraft.  Band  2,  p.  85.  Wiirzburg,  1903. 


122  THE  NUTRITION   OF  MAN 

of  work,  and  found  that  the  proteid  consumed  could  not 
have  furnished,  at  the  most,  more  than  one-half  the  energy 
required  to  lift  the  weights  of  their  bodies  to  the  top  of 
the  high  peak.  Further,  they  observed  that  neither  dur- 
ing the  work  period,  nor  immediately  after,  was  there  any 
noticeable  increase  in  the  excretion  of  nitrogen.  Obviously, 
as  they  state,  the  oxidation  of  proteid  matter  in  the  body 
cannot  be  the  exclusive  source  of  the  energy  of  muscular 
contraction,  since  the  measurable  amount  of  external  work 
performed  in  the  ascent  of  the  mountain  was  far  greater  than 
the  equivalent  of  the  energy  capable  of  being  furnished  by 
the  proteid  actually  burned.  To  which  may  be  added  the 
fact  that  considerable  energy,  not  measurable  in  their  ex- 
periment, must  have  been  employed  in  the  work  of  the 
involuntary  muscles  of  the  body ;  thus  increasing  by  so  much 
the  difference  between  the  muscular  work  actually  accom- 
plished and  the  available  energy  from  proteid  consumed.  Ifc 
is  true  that  minor  criticisms  regarding  certain  details  of  the  ex- 
periment can  be  offered  to-day,  such  as  the  fact  that  the  men 
were,  in  a  measure,  in  a  state  of  "nitrogen  starvation,"  etc., 
but  these  criticisms  do  not  in  any  degree  militate  against  the 
main  thesis  that  the  energy  of  muscular  contraction  does  not 
come  exclusively  from  the  consumption  or  breaking  down  of 
proteid,  either  of  food  or  tissue.  Vigorous  and  even  severe 
muscular  work  does  not  necessarily  increase  the  decomposi- 
tion of  proteid  material.  Dogs  made  to  run  in  large  tread- 
mills, with  the  same  diet  as  on  resting  days,  were  found  to 
excrete  practically  no  more  nitrogen  than  during  the  days  of 
rest.  Occasionally,  however,  in  some  one  experiment  the 
output  of  nitrogen  would  show  an  increase  over  the  output 
on  resting  days.  Further,  experiments  made  with  horses  led 
to  essentially  the  same  result,  except  that  greater  increase 
in  the  excretion  of  nitrogen  was  observed  than  with  dogs. 
This  increase  in  nitrogen  output,  however,  as  a  concomitant 


SOURCE   OF  ENERGY   OF  MUSCLE   WORK      123 

of  increased  muscular  activity,  could  be  prevented  by  adding 
to  the  amount  of  carbohydrate  food. 

While  experiments  of  this  nature,  on  man  and  animals,  all 
tended  to  show  little  or  no  increase  in  the  excretion  of  nitro- 
gen, as  a  result  of  muscle  work ;  and  likewise  no  increase  in 
the  output  of  sulphur  and  phosphorus,  thus  strengthening 
the  view  that  muscular  energy  is  not  the  result  of  proteid 
disintegration,  there  was  observed  marked  increase  in  the 
consumption  of  oxygen,  and  in  the  excretion  of  carbon  dioxide. 
Non-nitrogenous  matter  was  thus  at  once  suggested  as  the 
material  with  which  muscle  chiefly  does  its  work.  There  is 
to-day  no  question  of  the  general  truth  of  this  statement,  yet 
there  are  other  aspects  of  the  problem  to  be  considered  before 
we  can  lay  it  aside.  Pfliiger,  working  with  dogs,  and  Argu- 
tinsky,  experimenting  on  himself  by  arduous  mountain  climb- 
ing, reached  conclusions  seemingly  quite  opposed  to  what  has 
just  been  said.  Their  results,  however,  admit  of  quite  a 
different  interpretation  from  what  they  were  disposed  to  attach 
to  them.  Thus,  Pfliiger l  would  go  back  to  the  old  view  that 
all  muscle  work  is  at  the  expense  of  proteid  material,  because 
lean  dogs  fed  mainly,  or  entirely,  on  meat  and  made  to  do  an 
excessive  amount  of  work  were  found  by  him  to  excrete  ni- 
trogen somewhat  in  proportion  to  the  amount  of  work  done. 
Argutinsky,2  likewise,  in  his  mountain  climbing  carried  to  the 
point  of  fatigue,  and  with  a  high  proteid  intake  likewise,  saw 
in  the  increased  output  of  nitrogen  a  suggestion  of  the  same 
idea.  In  reality,  however,  their  results  merely  prove  that, 
under  some  circumstances,  proteid  may  serve  as  the  chief 
source  of  muscular  energy ;  as  when  the  body  is  poor  in  fat 
and  carbohydrate,  or  when  the  intake  consists  solely  of  pro- 
teid matter.  In  other  words,  muscular  work  may  result  in 


1  Pfliiger :  Die  Quelle  der  Muakelkraft.    Pfliiger's  Archiv  fiir  die  gesammte 
Physiologic,  Band  50,  p.  98. 

2  Argutinsky :  Muskelarbeit  und  Stickstoffumsatz.    Ibid.,  Band  46,  p.  552. 


124  THE  NUTRITION  OF  MAN 

an  increased  excretion  of  nitrogen  when  the  work  is  very 
severe,  and  there  is  not  a  corresponding  increase  in  the  fats 
or  carbohydrates  (fuel  ingredients)  of  the  food.  In  the 
words  of  Bunge,1  "we  might  assume  a  priori,  on  teleological 
grounds,  that  in  the  performance  of  its  most  important  func- 
tions the  organism  is  to  a  certain  extent  independent  of  the 
quality  of  its  food.  As  long  as  non-nitrogenous  food  is  sup- 
plied in  adequate  quantity  or  is  stored  up  in  the  tissues, 
muscular  work  is  chiefly  maintained  from  this  store.  When 
it  is  gone  the  proteids  are  attacked." 

There  is  no  question  that  the  energy  of  muscular  contrac- 
tion can  come  from  all  three  classes  of  organic  foodstuffs. 
Voluntary  muscular  movement  is  under  the  control  of  the  ner- 
vous system,  and  when  the  stimulus  is  applied  the  muscle  is 
bound  to  contract,  provided  of  course  there  is  sufficient 
energy-containing  material  present  to  furnish  the  means. 
Muscle  tissue,  like  other  tissues  and  organs,  has  a  certain 
power  of  adaptability,  by  which  it  is  able  to  do  its  work, 
even  though  it  is  not  adequately  supplied  with  its  preferred 
nutrient.  While  proteid  is  plainly  not  the  material  from 
which  the  energy  of  muscular  contraction  is  ordinarily  de- 
rived, it  is  equally  evident  that  in  emergency,  as  when  the 
usual  store  of  carbohydrate  and  fat  is  wanting,  proteid  can 
be  drawn  upon,  and  in  such  cases  vigorous  work  may  be 
attended  with  increased  nitrogen  output.  In  harmony  with 
this  statement,  we  find  on  record  in  recent  years  many  ex- 
periments, both  with  man  and  animals,  where  severe  mus- 
cular labor  is  accompanied  by  an  excretion  of  nitrogen  beyond 
what  occurs  on  days  of  rest;  but  by  simply  adding  to  the 
intake  of  non-nitrogenous  food  this  increased  outgo  of  nitro- 
gen is  at  once  checked.  With  moderate  work,  the  nitrogen 
outgo  is  rarely  influenced ;  it  is  only  when  the  work  becomes 


1  Bunge  :  Textbook  of  Physiological  and  Pathological  Chemistry.     Second 
English  Edition,  1902,  p.  352. 


SOURCE  OF  ENERGY  OF  MUSCLE  WORK      125 

excessive,  or  the  store  of  non-nitrogenous  reserve  is  small 
and  the  intake  of  the  latter  food  is  limited,  that  proteid 
matter  is  drawn  upon  to  supply  the  required  energy. 

Recalling  what  has  been  said  regarding  the  significance 
of  the  respiratory  quotient,  it  is  obvious  that  we  have  here 
a  means  of  acquiring  information  as  to  the  character  of  the 
material  that  is  burned  up  in  the  body  during  muscular  work. 
Increased  metabolism  of  carbohydrate  will  necessarily  result 
in  raising  the  respiratory  quotient,  and  if  the  latter  food 
material  alone  is  involved  the  respiratory  quotient  must 
naturally  approach  1. 0.  Zuntz,  however,  has  clearly  shown 
that  vigorous  muscular  activity  does  not  materially  change 
the  respiratory  quotient ;  except  in  cases  of  very  severe  work, 
where  the  oxygen-supply  of  the  muscles  is  interfered  with. 
Indeed,  the  muscles  may  be  made  to  do  work  sufficient  to 
increase  the  consumption  of  oxygen  threefold  or  more,  with- 
out any  change  in  the  respiratory  quotient  being  observed. 
And  as  there  is  frequently  no  change  whatever  in  the  output  of 
nitrogen  under  these  conditions,  it  follows  that  the  energy 
of  the  muscle  work  must  have  come  from  the  decomposition 
of  non-nitrogenous  material.  If  carbohydrates  alone  were 
involved,  the  respiratory  quotient  would  obviously  undergo 
change.  Since,  however,  this  remains  practically  stationary, 
we  are  led  to  the  conclusion  that  fat  must  be  involved  in 
large  degree,  in  addition  to  carbohydrate. 

In  this  connection,  it  is  a  significant  fact  that  with  fasting 
animals,  where  the  store  of  carbohydrate  material  is  more  or 
less  used  up,  severe  muscle  work  may  be  accomplished  with- 
out any  appreciable  increase  in  nitrogen  output,  thus  showing 
that  proteid  material  is  not  involved  and  clearly  pointing  to 
fat  as  the  source  of  the  muscular  energy.  Thus,  in  an  experi- 
ment referred  to  by  Leathes,  a  dog  on  the  sixth  and  seventh 
day  of  starvation  was  made  to  do  work  in  a  treadmill  equiva- 
lent to  climbing  to  a  height  of  1400  meters,  yet  the  output  of 


126 


THE  NUTRITION  OF  MAN 


nitrogen  was  increased  from  six  to  only  six  and  a  half  grams. 
Obviously,  not  much  of  the  energy  of  this  muscle  work  could 
have  come  from  the  breaking  down  of  proteid,  but  it  must 
have  been  derived  mainly  from  the  oxidation  of  fat.  There  is 
abundant  evidence  that  fat  can  be  used  as  a  source  of  energy 
by  muscles,  as  well  as  carbohydrates  and  proteids,  and  there 
is  every  reason  for  believing  that  the  yield  of  work  for  a  given 
amount  of  chemical  energy  in  the  form  of  fat  is  as  good  as  in 
the  case  of  either  of  the  other  two  substances.  In  fact,  the 
observations  of  Zuntz  show  that  fat  can  be  used  just  as 
economically  by  the  body  for  muscle  work  as  either  carbohy- 
drates or  proteid.  Thus,  in  one  experiment,1  he  determined 
the  oxygen-consumption  and  respiratory  quotient  in  a  man 
resting  and  working  on  three  different  diets  —  one  principally 
fat,  one  principally  carbohydrate,  and  the  other  principally 
proteid  —  and  found  that  slightly  less  oxygen  and  energy 
were  required  to  do  work  on  the  fat  diet  than  on  the  others. 
This  is  clearly  shown  in  the  following  table : 


Diet 
Principally. 

Resting. 

Working. 

Kilo- 
gram- 
meters 
of  Work 
Done. 

Per  Kilogram-meter 
of  Work. 

Oxygen 
Used  per 
Minute. 

Respira- 
tory 
Quotient. 

Oxygen 
Used  per 
Minute. 

Respira- 
tory 
Quotient. 

Oxygen 

Used. 

Calories. 

c.c. 

c.c. 

c.c. 

Fat 

319 

0.72 

1029 

0.72 

354 

2.01 

9.39 

Carbohydrate 

277 

0.90 

1029 

0.90 

346 

2.17 

10.41 

Proteid 

306 

0.80 

1127 

0.80 

345 

2.38 

11.35 

From  these  data,  we  see  that  per  kilogram-meter  of  work 
less  energy  was  required  and  less  oxygen  consumed  with  fat 
than  with  either  of  the  other  two  foodstuffs ;  but  practically, 
fat  and  carbohydrate  as  sources  of  muscle  energy  have  about 
the  same  value. 


Quoted  from  Leathes  :  Problems  in  Animal  Metabolism,  p.  100. 


SOURCE   OF  ENERGY  OF  MUSCLE  WORK      127 


Much  stress  is  ordinarily  laid  upon  the  importance  of  a 
large  intake  of  proteid  food  whenever  the  body  is  called 
upon  to  perform  severe,  or  long-continued,  muscular  work ; 
but  in  view  of  what  has  been  stated  it  may  be  ques- 
tioned whether  there  is  any  real  physiological  justification 
for  such  custom.  The  pedestrian  Weston,1  who  in  1884 
walked  50  miles  a  day  for  100  consecutive  days,  was  found 
by  Blyth  during  a  period  of  five  days  to  consume  in  his  food 
37.2  grams  of  nitrogen  a  day,  while  he  excreted  only  35.3 
grams,  leaving  a  balance  of  1.9  grams  of  nitrogen  per  day 
apparently  stored  in  the  body.  His  daily  food  during  this 
period  was  composed  of  262  grams  of  proteid,  64.6  grams  of 
fat,  and  799  grams  of  carbohydrate,  with  an  estimated  fuel 
value  of  4850  calories.  Yet  he  performed  this  large  amount 
of  work  daily,  and  still  laid  by  a  certain  amount  of  proteid  on 
a  ration,  the  energy  value  of  which  would  not  ordinarily  be 
considered  high  for  the  muscular  work  to  be  done.  Fourteen 
years  prior  to  this,  Weston,  while  in  New  York,  was  care- 


Period. 

Occupation. 

Duration 
of  Test. 

Nitrogen. 

In 

Food 

In 

Urine. 

In 

Excre- 
ment. 

Gain  + 
or 

Loss  — 

Fore  period 

Comparative  rest 

days 

5 

grams 
22.0 

grams 
18.7 

grams 
1.4 

grama 

+  1.0 

Working  period 
After  period 

Walking  62  miles 
per  day 

Rest  

I5 

5 

13.2 

28.6 

21.6 
22.0 

1.6 

2.2 

-10.0 
+  4.4 

fully  studied  by  Dr.  Flint  during  a  period  of  15  days,  on 
5  of  which  he  walked  a  total  of  317  miles.     His  diet  was 


1  This  and  the  following  account  of  Weston  are  taken  from  Bulletin  No.  98, 
U.  S.  Department  of  Agriculture,  Office  of  Experiment  Stations.  The  effect  of 
severe  and  prolonged  muscular  work  on  food  consumption,  digestion,  and  me' 
tabolism.  By  W.  O.  Atwater  and  H.  C.  Sherman,  p.  13. 


128  THE  NUTIRTIOH  OF  MAN 

essentially  a  proteid  diet,  consisting  principally  of  beef  ex- 
tract, oatmeal  gruel,  and  raw  eggs.  Nitrogen  intake  and 
output  were  carefully  compared  during  the  days  of  rest  and 
during  the  days  of  work,  with  the  results  tabulated. 

In  this  case  it  will  be  noted  that  the  daily  ration  was  com- 
paratively small,  and,  further,  that  during  the  working  period 
the  subject  consumed  much  less  proteid  than  on  the  resting 
days.  Moreover,  when  we  remember  that  the  total  energy 
value  of  his  diet  must  have  been  quite  small,  it  is  not  at  all 
strange  that  in  the  laborious  task  of  walking  62  miles  a  day 
he  should  have  temporarily  drawn  upon  his  store  of  body 
proteid  to  the  extent  of  62.5  grams,  or  10  grams  of  nitrogen 
a  day.  Such  experiences,  however,  do  not  by  any  means 
constitute  proof  that  in  excessive  muscular  work  there  is 
need  for  the  consumption  of  correspondingly  increased  quan- 
tities of  proteid  food,  or  that  the  energy  of  muscular  work 
comes  preferably  from  the  breaking  down  of  proteid  material. 
Carbohydrate  and  fat  unquestionably  take  precedence  over 
proteid  in  this  respect,  and  we  may  accept  as  settled  the 
view  that  in  all  practical  ways  carbohydrate  and  fat  stand 
on  an  equal  footing  as  sources  of  muscular  energy.  Less 
clear,  perhaps,  is  the  question  as  to  how  these  two  radically 
different  types  of  organic  material  are  utilized  by  the  muscle. 
It  has  been  a  favorite  belief  among  some  physiologists  that 
the  contracting  muscle  makes  use  of  only  one  substance  as 
the  direct  source  of  its  energy,  and  that  this  substance  is  the 
sugar  dextrose.  This  view  would  seemingly  imply  that  fat 
and  proteid  must  undergo  alteration  prior  to  their  utilization 
by  the  muscle ;  that,  possibly,  the  carbon  of  the  fat  and  proteid 
is  transformed  into  sugar  before  the  muscle  can  make  use  of 
it.  So  far  as  fat  is  concerned,  this  view  is  not  supported  by 
the  facts  available,  since  experiments  show  that  the  heat  and 
energy  liberated  in  the  utilization  of  a  given  amount  of  fat 
in  muscle  work  are  in  harmony  with  the  energy  value  of  the 


SOURCE   OF  ENERGY  OF  MUSCLE   WORK      129 

fat;  in  other  words,  the  fat  is  apparently  burned,  or  oxidized, 
directly,  without  undergoing  previous  transformation  into  any 
form  of  carbohydrate ;  or,  if  transformation  does  occur,  under 
some  conditions,  it  must  take  place  within  the  muscle  and 
without  loss  of  energy.  The  practical  significance  of  these 
facts  is  at  once  apparent,  for  if  fat,  in  order  to  be  available  as 
a  source  of  muscle  energy,  must  first  undergo  conversion  into 
sugar,  it  would  be  far  more  economical  from  a  physiological 
standpoint  to  replace  the  fat  of  the  diet  with  carbohydrate  in 
any  attempt  to  provide  suitable  nourishment  for  the  work- 
ing muscle.  We  may  safely  conclude,  however,  that  fat  and 
carbohydrate,  as  previously  suggested,  are  in  reality  both 
capable  of  direct  metabolism  by  the  muscular  tissue,  and  that 
each  is  of  value  as  a  source  of  muscular  energy  in  proportion  to 
its  heat  of  combustion,  yielding  substantially  the  same  propor- 
tion of  its  potential  energy  in  the  form  of  mechanical  work. 

Regarding  the  utilization  of  proteid  as  a  source  of  energy 
by  the  muscle,  there  are  many  grounds  for  believing  that 
here  the  body  has  to  deal  with  certain  alterations,  before  the 
proteid  can  be  made  available.  We  may  indeed  conjecture 
the  transformation  of  a  non -nitrogenous  portion  of  the  pro- 
teid molecule  into  carbohydrate,  as  a  necessary  step  in  its 
utilization  for  muscle  work.  It  is  certainly  true  that  in  the 
ordinary  katabolic  processes,  through  which  proteid  passes, 
there  is  a  tendency  for  the  nitrogen-containing  portion  to  be 
quickly  split  off  and  eliminated,  leaving  a  carbonaceous  resi- 
due which  may  represent  as  much  as  80  per  cent  of  the  total 
energy  of  the  original  proteid.  This  so-called  carbon  moiety 
of  the  proteid  molecule  is  apparently  much  less  rapidly  oxi- 
dized than  the  nitrogenous  portion,  and  may  indeed  be  tem- 
porarily stored  in  the  body,  in  the  form  of  fat  or  carbohydrate.1 

1  See  Leo  Langstein  :  Die  Kohlehydratbildung  aus  Eiweiss.  Ergebnisse  der 
Physiologie,  Band  3,  Erster  Theil,  p.  456. 

See  also,  Llithje :  Zur  Frage  der  Zuckerbildung  aus  Eiweiss.  Archiv  fiir  d. 
gesammte  Physiologic,  Band  106,  p.  160, 

9 


130  THE  NUTRITION  OF  MAN 

We  have  very  convincing  proof  that  the  carbohydrate 
glycogen  can  be  formed  from  proteid.  Thus,  the  feeding 
of  proteid  to  warm-blooded  animals  may  be  accompanied 
by  an  accumulation  of  glycogen  in  the  liver.  This  is  inter- 
preted as  meaning  that  in  the  cleavage  of  proteid  by  diges- 
tion the  various  nitrogenous  products  formed  are  somewhere, 
probably  in  the  liver,  still  further  acted  upon ;  the  contained 
nitrogen  with  some  of  the  carbon  being  converted  into  urea, 
while  the  non-nitrogenous  residue  is  transformed  into  glyco- 
gen, or  sugar.  That  some  such  change  takes  place,  or,  more 
specifically,  that  carbohydrate  does  result  from  proteid  is 
more  strikingly  shown  in  human  beings  suffering  with  dia- 
betes. In  severe  forms  of  this  disease,  all  carbohydrate  food 
consumed  is  rapidly  eliminated  through  the  kidneys  in  the 
form  of  sugar,  the  body  having  lost  the  power  of  burning 
sugar.  If  such  a  person  is  placed  upon  a  diet  composed  ex- 
clusively of  proteid,  sugar  still  continues  to  be  excreted,  and 
there  is  observed  a  certain  definite  relationship  between  the 
nitrogen  output  and  the  excretion  of  sugar,  thus  implying 
that  they  have  a  common  origin. 

Further,  there  are  certain  drugs,  such  as  phloridzin, 
which,  when  introduced  into  the  circulation,  set  up  a  severe 
diabetes  and  glycosuria.  Dogs  treated  in  this  way,  fed 
solely  on  proteid  or  even  starved  for  some  time,  will  con- 
tinue to  excrete  sugar,  and  as  in  the  previous  instance, 
there  is  observed  a  certain  definite  ratio  between  the 
nitrogen  output  and  the  elimination  of  sugar;  thus  leading 
to  the  conclusion  that  both  arise  from  the  destruction  of 
the  proteid  molecule.  Careful  study  of  this  ratio  of  dex- 
trose to  nitrogen  has  led  Lusk  to  the  conclusion  that  full  58 
per  cent  of  the  proteid  may  undergo  conversion  into  sugar 
in  the  body.  Hence,  it  is  easy  to  see  how  in  muscle  work, 
when  proteid  is  the  sole  source  of  the  energy  of  muscular 
contraction,  the  work  accomplished  may  still  result  from  the 


SOUKCE   OF  ENEKGY  OF  MUSCLE  WOEK      131 

direct  oxidation  of  carbohydrate  material,  indirectly  derived 
from  the  proteid  molecule.  It  requires  no  argument,  how- 
ever, to  convince  one  that  such  a  procedure  for  the  normal 
individual  is  less  economical  physiologically  than  a  direct 
utilization  of  carbohydrate  and  fat,  introduced  as  such  and 
duly  incorporated  with  the  muscle  substance.  Consequently, 
in  the  nourishment  of  the  body  for  vigorous  muscular  work, 
there  is  reason  in  a  diet  which  shall  provide  an  abundance  of 
carbohydrate  and  fat;  proteid  being  added  thereto  only  in 
amounts  sufficient  to  meet  the  ordinary  requirements  of 
the  body  for  nitrogen  and  to  furnish,  it  may  be,  proper 
pabulum  for  the  development  of  fresh  muscle  fibres,  where, 
as  in  training,  effort  is  being  made  to  strengthen  the  muscle 
tissue  and  so  enable  it  to  do  more  work.  Increase  in  pro- 
teid food  may  help  to  make  new  tissue,  but  the  source  of 
the  energy  of  muscle  work  is  to  be  found  mainly  in  the 
breaking  down  of  the  non-nitrogenous  materials,  carbohy- 
drate and  fat. 

In  view  of  these  facts,  we  may  advantageously  consider 
next  the  real  significance  of  the  proteid  metabolism  of  the 
body.  As  we  have  seen,  a  meal  rich  in  proteid  leads  at  once 
—  within  a  few  hours  —  to  an  excretion  of  urea  equivalent 
to  full  50  per  cent  of  the  nitrogen  of  the  ingested  proteid, 
while  a  few  hours  later  finds  practically  all  of  the  nitrogen 
of  the  intake  eliminated  from  the  body.  Further,  it  is  to  be 
remembered  that  in  a  general  way  this  occurs  no  matter  what 
the  condition  of  the  body  may  be  at  the  time  and  no  matter 
how  large  or  small  the  amount  of  proteid  consumed.  In 
other  words,  there  is  practically  no  appreciable  storing  of 
nitrogen  or  proteid  for  future  needs,  —  at  least  none  that  is 
proportional  to  the  increase  in  nitrogen  intake,  even  though 
the  body  be  in  a  condition  approximating  to  nitrogen  starva- 
tion. Moreover,  it  is  to  be  recalled  that  the  increased  pro- 
teid metabolism  attendant  on  increased  intake  of  proteid  food 


132  THE  NUTRITION   OF  MAN 

is  accompanied  by  an  acceleration  of  the  metabolism  of  non- 
nitrogenous  matter;  thus  resulting  in  a  stirring  up  of  tissue 
change,  with  consequent  oxidation  and  loss  of  a  certain  pro- 
portion of  accumulated  fat  and  carbohydrate.  Coincident 
with  this  increased  excretion  of  nitrogen,  the  output  of 
carbon  dioxide  is  likewise  increased  somewhat,  due  as  is  be- 
lieved mainly  to  increased  metabolism  of  the  involuntary 
muscle  fibres  of  the  gastro-intestinal  tract,  by  action  of  which 
the  accelerated  peristalsis  so  characteristic  of  food  intake  is 
accomplished.  Further,  the  increased  output  of  carbon 
dioxide,  under  these  conditions,  is  to  be  attributed  also  to 
the  greater  activity  of  the  digestive  and  excretory  organs, 
naturally  stimulated  to  greater  functional  power  by  the 
presence  of  proteid  foods  and  their  decomposition  products. 
Still,  as  stated  by  Leathes,  "the  two  main  end-products  of 
proteid  metabolism,  urea  and  carbonic  acid,  are,  to  a  great 
extent,  produced  independently  of  each  other,  and  the  re- 
actions which  result  in  the  discharge  of  the  nitrogen  are  not 
those  in  which  energy  is  set  free,  work  done,  and  carbonic 
acid  produced."  In  other  words,  there  is  suggested  what 
we  have  already  referred  to,  viz. ,  that  in  proteid  metabolism 
a  nitrogenous  portion  of  the  proteid  molecule  is  quickly  split 
off  and  gotten  rid  of,  while  the  non-nitrogenous  part  may  be 
reserved  for  future  oxidation,  serving-  as  a  source  of  muscle 
energy  or  for  other  purposes.  This  being  so,  it  is  plain  that 
"proteid  metabolism  in  so  far  as  it  is  concerned  with  the 
evolution  of  energy,  proteid  metabolism  in  its  exothermic 
stages,  may  be  almost  entirely  non-nitrogenous  metabolism  " 
(Leathes). 

Is  there  any  advantage  to  the  body,  however,  in  this 
carbonaceous  residue  of  the  proteid  molecule  over  simple 
carbohydrate  and  fat?  Can  the  processes  of  the  body  be  ac- 
complished more  economcially,  or  more  advantageously,  with 
a  daily  diet  so  constructed  that  the  tissues  and  organs  must 


THEORIES   OF  PEOTEID  METABOLISM         133 

depend  mainly  upon  this  carbon  moiety  of  the  proteid  mole- 
r/ule  for  their  energy-yielding  material  ?  It  has  been  one  of 
the  physiological  dogmas  of  the  past,  that  the  tissues  and 
organs  of  the  body,  or  rather  their  constituent  cells,  preferred 
to  use  proteid  for  all  their  needs  whenever  it  was  available. 
If  proteid  were  wanting,  either  because  of  insufficient  intake, 
or  because  of  excessive  activity,  then  the  tissue  cells  would 
draw  upon  their  store  of  non-nitrogenous  material.  Food 
proteid  and  tissue  proteid,  however,  were  the  materials  pre- 
ferred by  the  organism,  so  ran  the  argument,  and  the  large  and 
incessant  output  of  nitrogen  which  accompanied  the  intake  of 
proteid  was  accepted  as  proof  of  the  general  truth  of  this  idea. 
We  might  well  question  wherein  lies  the  great  advantage 
to  the  body  in  this  continual  excretion  of  nitrogen ;  whether 
the  loss  of  energy  in  handling  and  removing  the  nitrogenous 
portion  of  the  necessarily  large  proteid  intake,  in  order  to 
render  available  the  non-nitrogenous  part  of  the  molecule, 
might  not  more  than  compensate  for  the  supposed  gain  ?  But 
the  truly  astonishing  fact  that  the  output  of  nitrogen  runs 
parallel  with  the  intake  of  proteid,  that  the  body  cannot  store 
up  nitrogen  to  any  large  extent,  has  been  taken  as  conclusive 
evidence  that  the  organism  prefers  to  use  proteid  for  all  of  its 
requirements.  Truly,  we  might  just  as  well  argue  that  this 
significant  rise  in  the  excretion  of  nitrogen  after  partaking  of 
a  proteid  meal  is  an  indication  that  the  body  has  no  need  of 
this  excess  of  nitrogen;  that  it  is  indeed  a  possible  source 
of  danger,  since  the  system  strives  vigorously  to  rid  itself  of 
the  surplus,  and  that  the  energy -needs  of  the  body  can  be 
much  more  advantageously  and  economically  met  from  fat 
and  carbohydrate  than  from  the  carbonaceous  residue  result- 
ing from  the  disruption  of  the  proteid  molecule. 

In  discussing  these  questions,  we  shall  need  to  refer  to 
several  of  the  current  theories  concerning  proteid  metabolism, 
notably,  the  theories  of  Voit,  Pfluger,  and  Folin.  In  1867 


134  THE  NUTRITION  OF  MAN 

Carl  Voit,1  of  Munich,  advanced  the  view  that  the  proteid 
material  of  the  body  exists  in  two  distinct  forms,  viz.,  as 
"morphotic"  or  " organized"  proteid,  representing  proteid 
which  has  actually  become  a  part  of  the  living  units  of  the 
body,  i.  e.,  an  integral  part  of  the  living  tissues;  and  "cir- 
culating "  proteid,  or  that  which  exists  in  the  internal  meshes 
of  the  tissue,  or  in  the  surrounding  lymph  and  circulating 
blood.  The  real  point  of  distinction  here  is  that  while  one 
portion  of  the  body  proteid  is  raised  to  the  higher  plane  of 
living  matter,  i.  e.,  becomes  a  component  part  of  the  living 
protoplasm,  another  and  perhaps  larger  portion  is  outside  of 
the  morphological  framework  of  the  tissue,  constituting  a 
sort  of  internal  medium  which  bathes  the  living  cells,  and 
acts  as  middleman  between  the  blood  and  lymph  on  the  one 
side  and  the  living  cells  on  the  other.  According  to  Voit's 
view,  it  is  this  circulating  proteid  that  undergoes  metabolism ; 
the  proteid  of  the  food  after  digestion  and  absorption  being 
carried  to  the  different  tissues  and  organs,  and  then,  without 
becoming  an  integral  part  of  the  living  protoplasm  of  the 
cells,  it  is  broken  down  under  the  influence  of  the  latter. 
Obviously,  small  numbers  of  tissue  cells  are  constantly 
dying,  their  proteid  matter  passing  into  solution,  where  it 
likewise  undergoes  metabolism.  In  other  words,  according 
to  Voit,  the  great  bulk  of  the  proteid  undergoing  katabolism 
is  the  circulating  proteid,  derived  more  or  less  directly  from 
the  food,  and  which  at  no  time  has  been  a  part  of  the  tissue 
framework;  while  a  smaller,  but  more  constant  amount, 
represents  the  breaking  down  of  tissue  cells.  This  concep- 
tion of  proteid  metabolism  is  akin  to  our  conception  of  mor- 
phological and  physiological  destruction.  In  the  words  of 
Foster:  "We  know  that  an  epithelial  cell,  as  notably  in  the 
case  of  the  skin,  may  be  bodily  cast  off  and  its  place  filled 


1  See  Voit:  Hermann's  Handbuch  der  Physiologic,  Band  6,  p.  301. 


THEORIES   OF  PEOTETD  METABOLISM         135 

by  a  new  cell ;  and  probably  a  similar  disappearance  of  and 
renewal  of  histological  units  takes  place  in  all  the  tissues  of 
the  body  to  a  variable  extent.  But  in  the  adult  body  these 
histological  transformations  are,  in  the  cases  of  most  of  the 
tissues,  slow  and  infrequent.  A  muscle,  for  instance,  may 
suffer  very  considerable  wasting  and  recover  from  that  wast- 
ing without  any  loss  or  renewal  of  its  elementary  fibres. 
And  it  is  obvious  that  the  metabolism  of  which  we  are  now 
speaking  does  not  involve  any  such  shifting  of  histological 
units.  On  the  other  hand,  we  find  these  histological  units, 
the  muscle  fibre  or  the  gland  cell,  for  instance,  living  on 
their  internal  medium,  the  blood,  or  rather  on  the  lymph, 
which  is  the  middleman  between  themselves  and  the  actual 
blood  flowing  in  the  vascular  channels." 

Voit  claims  that  the  proteid  dissolved  in  the  fluids  of  the 
body  is  more  easily  decomposable  than  that  which  exists  com- 
bined in  organized  form,  or  as  more  or  less  insoluble  tissue 
proteid;  and  it  is  this  soluble  and  circulating  form  which, 
under  the  influence  of  the  living  cells,  undergoes  destruction 
or  metabolism.  We  know,  as  has  been  previously  stated, 
that  oxidation  does  not  take  place  to  any  extent  in  the 
circulating  blood,  and  similarly  there  is  every  reason  for 
believing  that  proteid  metabolism  does  not  occur  in  this 
menstrum.  Metabolism  is  limited  mainly  to  the  active 
tissues  of  the  body,  but  according  to  the  present  concep- 
tion of  the  matter  it  does  not  occur  at  the  expense  of 
the  proteid  of  the  living  cells,  but  involves  material  con- 
tained in  the  fluids  bathing  the  cells;  i.  e.,  it  is  not  the 
organized  proteid  that  undergoes  metabolism,  but  the  proteid 
circulating  in  and  about  the  internal  meshes  of  the  cells  and 
tissues,  the  living  cell  being  the  active  agent  in  controlling 
the  process.  Further,  this  view  lessens  the  difficulty  of 
understanding  the  elimination  of  nitrogen  after  a  meal  rich 
in  proteid.  If  it  was  necessary  to  assume  that  all  the  proteid 


136  THE  NUTKITION   OF  MAN 

of  our  daily  food  is  built  up  into  living  protoplasm  before 
katabolism  occurs,  it  would  be  exceedingly  difficult  to  ex- 
plain the  sudden  and  rapid  elimination  of  nitrogen  which 
follows  the  ingestion  of  proteid.  For  example,  we  can 
hardly  imagine  that  merely  eating  an  excess  of  proteid  food 
will  lead  to  an  actual  breaking  down  of  the  living  framework 
of  the  tissues,  equivalent  to  the  amount  of  nitrogen  which  the 
body  at  once  eliminates.  Voit's  theory,  on  the  other  hand, 
supposes  a  twofold  origin  of  the  nitrogen  excreted ;  one  part, 
the  larger  and  variable  portion,  comes  from  the  direct  metabo- 
lism of  the  circulating  proteid,  being  the  immediate  result  of 
the  ingested  food  and  varying  in  amount  with  the  quantity 
of  proteid  food  consumed;  the  other,  smaller  and  less  vari- 
able in  amount,  has  its  origin  in  the  metabolism  of  the 
true  tissue  proteid,  or  the  actual  living  framework  of  the 
body. 

In  a  fasting  animal,  the  tissues  and  organs  of  the  body  still 
contain  a  large  proportion  of  proteid  matter,  yet  only  a  small 
fraction  of  this  proteid  is  eliminated  each  day,  hardly  1  per 
cent.  If,  however,  proteid  is  absorbed  from  the  intestine, 
proteid  metabolism  is  at  once  increased,  and  the  excretion  of 
nitrogen  may  be  fifteen  times  greater  than  during  hunger. 
In  other  words,  the  extent  of  proteid  metabolism  is  not  at 
all  proportional  to  the  total  amount  of  proteid  contained  in. 
the  body  as  a  whole,  but  runs  parallel  in  a  general  way  with 
the  quantity  of  proteid  absorbed  from  the  intestine.  Ob- 
viously, the  newly  absorbed  proteid  is  quite  different  in 
nature  from  the  proteid  which  in  much  larger  amounts  is 
deposited  throughout  the  body,  since  it  is  not  organized  and 
is  so  much  more  easily  decomposable  (Voit).  This  is  the 
circulating  proteid  of  the  body ;  it  exists  in  solution,  and  it  is 
a  significant  fact  that,  according  to  Voit,  the  chemical  trans- 
formations that  characterize  proteid  katabolism  occur  only  in 
solution.  The  organized  proteid,  on  the  other  hand,  is  in 


THEORIES   OF  PEOTEID  METABOLISM         137 

a  state  of  suspension,  and  its  katabolism,  which  is  relatively 
very  small,  is  preceded  by  solution  of  the  proteid  in  the 
fluids  of  the  tissue,  after  which  its  further  breaking  down  is 
assumed  to  be  the  same  as  that  of  the  circulating  proteid. 
This  latter  view  is  a  fundamental  part  of  the  Voit  theory ;  in 
long-continued  fasting,  for  example,  the  living  protoplasm 
of  the  various  tissues  and  organs  is  of  necessity  drawn  upon 
for  the  nourishment  of  the  more  vital  parts  of  the  body,  such 
as  the  brain,  spinal  cord,  etc.,  consequently  the  organized  pro- 
teid is  gradually  dissolved  and  then  decomposed,  after  it  has 
become  liquefied  and  has  thus  lost  its  organized  structure. 

In  this  conception  of  proteid  metabolism,  we  picture  the 
different  organs  and  tissues  of  the  body  as  being  permeated 
by  a  fluid  which  carries  variable  amounts  of  nutritive  mate- 
rial, the  quantity  of  the  latter  determining  in  a  way  the  ex- 
tent of  the  proteid  katabolism  which  shall  take  place.  As 
the  proteid  of  the  food  passes  into  the  blood  and  lymph,  the 
fluids  bathing  the  cells  are  correspondingly  enriched,  and  as 
a  result,  proteid  katabolism  is  accelerated  in  parallel  degree. 
During  hunger,  on  the  other  hand,  the  organized  proteid  of 
the  tissue  cells  is  gradually  liquefied  and  passes  out  into  the 
current  of  the  circulating  fluids.  As  before  stated,  the  or- 
ganized proteid  as  such  is  never  decomposed;  it  must  first 
enter  into  solution,  and  then  under  the  influence  of  the  living 
cells  it  undergoes  disruption  in  the  same  manner  as  the  cir- 
culating proteid.  It  is  thus  evident  that  the  tissue  cells  and 
the  circulating  fluids  permeating  them  bear  an  ever  changing 
relationship  to  each  other.  Excess  of  circulating  proteid  will 
be  attended  by  increased  katabolism,  while  at  the  same  time 
there  may  be  some  accumulation  of  proteid  in  the  cells,  and 
indeed  some  conversion  into  organized  proteid.  During  fast- 
ing, hunger,  or  with  an  insufficient  intake  of  proteid  food, 
the  current  will  naturally  be  in  the  opposite  direction,  and 
organized  proteid  will  slowly,  but  surely,  be  drawn  upon. 


138  THE  NUTRITION   OF  MAN 

Again,  we  may  ask  in  view  of  these  facts,  of  what  real  use 
to  the  body  is  this  large  katabolism  of  circulating  proteid? 
We  can  easily  understand  the  need  of  proteid  to  supply  the 
loss  incidental  to  the  breaking  down  of  organized  or  true 
tissue  proteid,  but  this  we  are  led  to  believe  is  very  small 
in  amount.  Is  there  any  real  need  for  proteid  beyond  this 
requirement?  The  physiological  fuel  value  of  proteid  is  no 
greater  than  that  of  carbohydrate  and  considerably  less  than 
half  that  of  fat,  consequently  there  is  on  the  surface  no 
apparent  reason  why  proteid  should  be  used  for  its  energy 
value  in  preference  to  the  non-nitrogenous  foodstuffs.  Fur- 
ther, as  we  Lave  seen,  the  energy  of  muscle  work  comes 
mainly,  at  least,  from  the  breaking  down  of  fat  and  carbohy- 
drate; proteid,  in  the  case  of  the  well-nourished  individual, 
ordinarily  playing  no  part  in  this  important  line  of  energy 
exchange.  Lastly,  in  the  katabolism  of  proteid  there  is 
the  large  proportion  of  nitrogenous  matter  to  be  split  off  and 
disposed  of  before  the  carbon  moiety  of  the  molecule  can  be 
rendered  available.  Here,  we  have  involved  not  only  a  loss 
of  energy,  but  in  addition  a  certain  amount  of  what  appears 
to  be  useless  labor  thrown  upon  the  liver,  kidneys,  and  other 
organs.  Is  there  any  wonder  that  the  thoughtful  physiolo- 
gist, looking  at  the  facts  and  theories  presented  by  the  Voit 
conception  of  proteid  katabolism,  should  ask  wherein  lies  the 
value  to  the  body  of  this  high  rate  of  metabolism  of  circulat- 
ing proteid,  a  rate  of  metabolism  which  is  seemingly  governed 
primarily  by  the  amount  of  proteid  food  ingested  ? 

Turning  next  to  Pfliiger's  I  views  regarding  proteid  katabo- 
lism, we  find  a  totally  different  outlook.  Here,  the  supposi- 
tion prevails  that  the  plasma  of  the  blood  and  lymph,  with 
its  contained  proteid,  is  the  food  of  the  organs  or  their  cells, 


1  Eduard  Pfluger:  Ueber  einige  Gesetze  des  Eiweissstoffwechsels  (mit  beson- 
derer  Beriicksichtigung  der  Lehre  vom  sogenannten  "  circulirinden  Eiweiss  "). 
Archiv  f.  d.  gesammte  Fhysiologie,  Band  54,  p.  333. 


THEOEIES   OF  PBOTEID  METABOLISM         139 

but  that  before  this  food  material  can  undergo  katabolism  it 
must  first  be  absorbed  by  the  cell  and  built  up  into  the  living 
protoplasm  of  the  tissue.  In  other  words,  according  to  the 
views  expressed  by  Pfliiger,  katabolism  must  be  preceded  by 
organization  of  the  proteid.  Expressed  in  still  different 
language,  the  proteid  material  circulating  in  blood  and 
lymph  must  be  eaten  up  by  the  hungry  cells  and,  by  appro- 
priate anabolic  processes,  made  an  integral  part  of  the  living 
protoplasm  before  disassimilation  can  occur.  Further,  ac- 
cording to  Pfluger's  conception  of  these  processes,  there  is  a 
radical  difference  in  the  chemical  nature  of  living  protoplasm 
as  compared  with  that  of  the  so-called  circulating  proteid. 
The  latter  is  looked  upon  as  being  comparatively  stable,  re- 
sisting oxidation  in  high  degree,  and  hence  not  prone  to 
undergo  metabolism.  Living  protoplasm,  on  the  other  hand, 
is  characterized  by  instability,  suffering  oxidation  with  the 
greatest  ease,  and  hence  readily  broken  down  in  the  ordinary 
processes  of  katabolism.  Assuming  for  the  moment  the  cor- 
rectness of  this  theory,  we  see  at  a  glance  that  all  disruption 
of  proteid  matter  in  the  body  must  be  preceded  by  the  up- 
building of  the  proteid  into  living  protoplasm.  There  can 
be  no  destruction  of  proteid  until  the  latter  has  been  raised 
to  the  high  plane  of  living  matter.  The  dead,  inert  circulat- 
ing proteid  can  serve  simply  as  food  for  the  living  cells,  and 
cannot  undergo  katabolism  until  it  has  been  built  up  into  the 
organized  structure  of  the  tissue  or  organ.  Even  though  we 
grant  that  a  small  proportion  of  proteid  may  suffer  katabolism 
without  previous  organization,  it  does  not  materially  modify 
the  general  trend  of  the  argument  that,  according  to  Pfliiger's 
hypothesis,  proteid  katabolism  is  essentially  a  process  involv- 
ing the  disruption  of  living  protoplasm. 

Consider  what  this  means  in  the  light  of  facts  already 
presented.  Remembering  that  the  one  factor  above  all  others 
influencing  the  rate  of  proteid  katabolism  is  the  amount  of 


140  THE  NUTRITION  OF   MAN 

proteid  food  Ktaken  in,  and  that  the  output  of  nitrogen,  no 
matter  what  the  previous  condition  of  the  body  or  the 
amount  of  proteid  food  ingested,  runs  more  or  less  parallel 
with  the  consumption  of  proteid,  we  are  forced  to  the  con- 
clusion, in  accepting  this  hypothesis,  that  there  must  be 
superhuman  activity  in  the  building  up  of  living  protoplasm, 
only  to  be  followed,  however,  by  its  immediate  and  more  or 
less  complete  breaking  down.  Further,  think  of  the  daily 
or  periodical  fluctuation  in  the  construction  of  bioplasm, 
coincident  with  variations  in  the  amount  of  proteid  food 
consumed,  and  the  corresponding  destruction  of  bioplasm 
as  indicated  by  the  daily  output  of  nitrogen.  Imagine, 
if  you  will,  the  concrete  case  of  a  man  of  70  kilos  body- 
weight  eating  a  daily  ration  containing  125  grams  of  proteid, 
the  nitrogen  equivalent  of  which  is  practically  excreted 
within  twenty-four  hours,  and  are  we  not  wise  in  hesitating 
to  believe  that  all  of  that  proteid  has  been  so  quickly 
built  up  into  living  or  organized  tissue  only  to  be  imme- 
diately broken  down  and  thrown  out  of  the  body?  Think 
of  the  enormous  activity  implied  in  the  manufacture  of  this 
bioplasm  in  the  time  allotted,  and  for  what?  Apparently, 
so  that  it  can  be  broken  down  again.  But  such  energy  as 
is  liberated  in  the  breaking-down  process  might  be  derived 
far  more  economically  by  simple  destruction  of  the  proteid, 
as  contained  in  the  meshes  of  the  tissue  elements,  without 
assuming  a  preliminary  conversion  into  living  protoplasm. 
Obviously,  we  have  here  a  theory  which  does  not  help  us  in 
arriving  at  any  very  satisfactory  conception  of  proteid  metab- 
olism. The  facts  which  Pfliiger  and  his  followers  bring 
forward  in  support  of  the  theory  are  not  very  convincing,  or 
at  least  not  sufficiently  so  to  carry  conviction  in  the  face  of 
a  natural  disinclination  to  believe  in  the  necessity  of  such  a 
profound  anabolic  process,  merely  as  a  prelude  to  the  speedy 
destruction  of  the  finished  product.  Finally,  we  may  add 


THEORIES   OF  PROTEID  METABOLISM          141 

that  if  all  proteid  katabolized  in  the  body  must  first  be  raised 
to  the  high  level  of  living  protoplasm  before  the  final  disrup- 
tion can  occur,  it  may  be  prudent  to  keep  the  daily  intake 
of  this  foodstuff  down  to  a  level  somewhat  commensurate 
with  the  real  needs  of  the  body. 

As  has  been  stated  many  times  in  the  course  of  this  pres- 
entation, the  most  striking  feature  of  proteid  metabolism  is 
the  rapidity  with  which  large  quantities  of  proteid  consumed 
as  food  are  broken  down,  and  the  contained  nitrogen  elimi- 
nated from  the  body  as  urea.  A  few  hours  will  suffice  to 
accomplish  the  more  or  less  complete  destruction  of  food 
proteid ;  and  any  theory  of  proteid  metabolism,  to  be  at  all 
satisfactory,  must  explain  this  peculiar  phenomenon.  Accord- 
ing to  recent  investigations,  it  seems  probable  that  some,  at 
least,  of  the  cleavage  products  of  proteid  formed  during  in- 
testinal digestion  are  not  built  up  into  new  proteid,  but  are  at 
once  eliminated  mainly  in  the  form  of  urea,  without  becoming 
a  part  of  either  the  so-called  circulating  proteid,  or  the  living 
protoplasm  of  the  body.  It  will  be  recalled  that  under  the 
influence  of  the  digestive  enzymes,  trypsin  and  erepsin,  pro- 
teid foodstuffs  may  be  broken  down  while  undergoing  in- 
testinal digestion  into  monamino-  and  diamino-acids,  such 
as  leucin,  tyrosin,  arginin,  lysin,  etc.  A  certain  proportion 
of  these  comparatively  simple  substances  may  be  directly 
absorbed  by  the  portal  circulation  and  carried  to  the  liver, 
where  they  may  undergo  conversion  into  urea.  In  this  way, 
some  portion  of  the  nitrogen  of  the  ingested  food  may  be 
quickly  eliminated  from  the  system.  As  has  been  stated  in 
another  connection,  we  are  not  sure  at  present  how  far  pro- 
teid decomposition  of  the  kind  indicated  takes  place  normally 
in  the  body.  We  merely  know  that  there  are  present  in  the 
intestine,  enzymes  capable  of  splitting  up  proteid  into  these 
small  fragments,  and  that  substances  of  this  type  when  made 
to  circulate  through  the  liver  are  transformed  into  urea.  These 


142  THE  NUTEITION  OF  MAN 

facts,  coupled  with  the  well-known-  tendency  of  the  nitrogen 
of  proteid  food  to  appear  in  the  excretions  a  few  hours  after 
the  food  in  question  has  been  consumed,  naturally  suggests 
a  direct  breaking  down  of  proteid  along  the  lines  indicated, 
with  a  possible  retention  of  a  carbonaceous  residue  (nitrogen- 
free)  for  subsequent  oxidation,  as  a  source  of  energy  for  heat 
or  work.  Obviously,  all  of  the  proteid  food  cannot  behave 
in  this  manner,  for  if  such  were  the  case  there  would  be  no 
proteid  available  for  making  good  the  normal  waste  incidental 
to  tissue  changes.  Either  a  certain  amount  of  proteid  es- 
capes this  profound  alteration  produced  by  the  proteolytic 
enzymes  in  question,  or  else  a  certain  proportion  of  these 
simple  decomposition  products  is  synthesized  in  the  intestine, 
or  in  the  tissues  of  the  body,  to  form  new  proteid  for  the 
regeneration  of  cell  protoplasm.  However  this  may  be,  we 
have  presented  in  this  view  a  plausible  explanation  of  the 
prompt  appearance  of  food  nitrogen  in  the  excretions,  and 
without  compelling  belief  in  a  theory,  such  as  Pfliiger's, 
which  taxes  one's  credulity  to  the  utmost.  To  be  sure,  as  a 
prominent  writer  on  physiology  has  recently  said,  such  a  view 
stands  opposed  to  our  conceptions  of  the  importance  of  pro- 
teid food;  but  it  seems  possible,  in  the  light  of  accumulating 
knowledge,  that  our  conceptions  of  the  part  played  by  proteid 
foods  in  the  nutrition  of  man  have  not  been  strictly  logical, 
or  quite  in  accord  with  true  physiological  reasoning. 

Again,  in  this  connection,  we  may  ask  the  question,  why  is 
it  that  the  body  provides  such  an  effective  method  for  the 
speedy  breaking  down  of  proteid  food  and  the  prompt  elim- 
ination of  the  contained  nitrogen  ?  Whatever  the  means  made 
use  of  by  the  organism  in  accomplishing  this,  the  result  is  the 
same ;  the  nitrogen  of  the  ingested  food  is,  in  large  measure, 
quickly  gotten  rid  of.  We  clearly  recognize  the  all-important 
position  of  proteid  foods  in  the  nutrition  of  the  body,  but 
there  appears  a  certain  inconsistency  in  this  prompt  removal 


THEORIES   OF  PKOTEID  METABOLISM          143 

of  the  nitrogen-containing  portion  of  the  proteid  molecule. 
The  nitrogenous  part  of  the  proteid  food  is,  physiologically 
considered,  the  all-important  part.  It  is  the  only  source  of 
nitrogen  available  to  the  system,  and  yet  apparently  the  larger 
proportion  of  this  nitrogenous  material  is  not  utilized  in  any 
recognizable  way,  but  is  eliminated  as  quickly  as  possible.  Is 
it  not  within  the  limits  of  possibility  that  these  methods, 
whatever  may  be  the  exact  mechanism  involved,  are  merely 
a  means  of  getting  rid  of  a  surplus  of  proteid  for  which  the 
body  has  no  real  need  ?  This  question  I  shall  try  to  answer 
later  on  in  another  connection,  but  we  may  advantageously 
keep  this  possibility  in  mind  while  we  are  discussing  these 
theories  of  proteid  metabolism. 

It  is  obvious,  in  the  light  of  present  knowledge,  that  there 
must  be  a  certain  amount  of  true  tissue  proteid  broken  down 
each  day,  independent  of  that  larger  metabolism  coincident 
with  the  intake  of  proteid  food.  However  much  this  more 
voluminous  proteid  katabolism  may  fluctuate,  owing  to  varia- 
tions in  the  intake  of  proteid,  and  whatever  the  significance  of 
this  latter  phase  of  metabolism,  it  is  self-evident  that  there 
must  be  a  steady,  constant  metabolism,  upon  which  the  life 
of  the  various  tissues  and  organs  of  the  body  depends,  and  by 
which  the  proteid  integrity  of  the  tissue  cells  is  maintained. 
This  implies  a  certain  degree  of  true  tissue  change,  in  which 
definite  amounts  of  proteid  material  are  broken  down  and 
the  resultant  loss  made  good  from  the  proteid  intake.  No 
matter  what  specific  name  be  applied  to  this  form  of  pro- 
teid katabolism,  its  existence  is  clearly  recognized.  It  is  ob- 
viously a  form  of  metabolism  distinct,  and  probably  quite 
different,  from  that  form,  more  variable  in  extent,  which  is 
associated  with  the  intake  of  proteid  food.  Plainly,  if  there 
is  truth  in  these  statements,  there  should  be  some  data  avail- 
able by  means  of  which  these  two  lines  of  proteid  katabolism 
can  be  more  or  less  sharply  differentiated. 


144 


THE  NUTRITION  OF  MAN 


Thanks  especially  to  the  work  of  Folin,1  these  data  are  now 
apparently  at  hand,  and  the  facts  which  he  has  accumulated 
with  painstaking  care  seem  destined  to  throw  additional 
light  upon  our  conception  of  proteid  metabolism.  It  will 
be  remembered  that  in  the  breaking  down  of  proteid,  the 
great  bulk  of  its  contained  nitrogen  is  eliminated  in  the 
form  of  urea.  In  addition,  a  certain  smaller  amount  of  ni- 
trogen is  excreted  in  the  forms  of  creatinin  and  uric  acid. 
As  we  have  seen,  the  total  output  of  nitrogen,  which  meas- 
ures the  extent  to  which  proteid  is  decomposed  in  the  body, 
varies  with  the  intake  of  proteid  food  ;  but  it  is  found  that 
the  proportion  of  nitrogen  excreted  in  the  forms  of  urea  and 
uric  acid  varies  with  the  extent  of  the  metabolism.  In  other 
words,  quantitative  changes  in  the  daily  proteid  katabolism 
are  accompanied  by  pronounced  changes  in  the  distribution 
of  the  excreted  nitrogen.  Let  us  take  a  single  illustration 
from  Folin 's  results ;  the  case  of  a  healthy  man  who  on  one 
day  —  July  13  —  consumed  a  proteid-rich  diet,  and  on  the 
other  day  —  July  20  —  was  living  on  a  diet  containing  only 
about  1  gram  of  nitrogen.  The  composition  of  the  excretion 
through  the  kidneys  on  these  two  days  is  shown  in  the 
following  table: 


July  13. 

July  20. 

Volume  of  urine  .    .    . 

1170  c.c. 

385  c.c. 

Total  nitrogen      .    .    . 

16.80  grams 

3.60  grams 

Urea-nitrogen  .... 

14.70     "      =  87.5% 

2.20     "      =61.7% 

Uric  acid-nitrogen    .    . 

0.18     "      =    1.1% 

0.09      "      =    2.5% 

Creatinin-nitrogen    .    . 

0.58     "      =    3.6% 

0.60     "      =  17.2% 

1  Otto  Folin :  Laws  Governing  the  Chemical  Composition  of  Urine.  American 
Journal  of  Physiology,  vol.  13,  p.  66.  A  theory  of  Protein  Metabolism.  Ibid., 
vol.  13,  p.  117. 


THEOEIES   OF  PEOTEID  METABOLISM         145 

Here  we  see,  as  would  be  expected,  that  on  the  high  pro- 
teid  diet,  there  was  a  large  excretion  of  total  nitrogen  and  of 
urea ;  while  on  the  low  proteid  diet,  nitrogen  and  urea  were 
correspondingly  diminished.  The  point  to  attract  our  atten- 
tion, however,  is  the  marked  difference  in  the  percentage  of 
urea-nitrogen  in  the  two  cases;  a  difference  which  amounts 
to  about  26  per  cent.  A  similar  difference  is  to  be  noted  in 
the  percentage  of  uric  acid-nitrogen.  Lastly,  it  is  to  be  ob- 
served that  in  spite  of  the  great  difference  in  the  extent  of 
metabolism  on  the  two  days  —  an  excretion  of  16.8  grams 
of  nitrogen,  as  contrasted  with  3.6  grams  — the  amount  of 
creatinin-nitrogen  is  essentially  the  same.  Folin  finds  that 
these  peculiarities  in  the  percentage  distribution  of  excreted 
nitrogen  hold  good  in  all  cases  where  there  is  this  wide 
divergence  in  the  amount  of  proteid  katabolized,  and,  fur- 
ther, that  there  is  a  gradual  and  regular  transition  from  the 
one  extreme  to  the  other.  He  sees  in  these  results  evidence 
that  there  are  in  the  body  two  forms  of  proteid  katabolism, 
essentially  independent  and  quite  different.  One  kind  is 
extremely  variable  in  quantity,  while  the  other  tends  to  re- 
main constant.  The  variable  form  has  its  own  particular 
kind  of  waste  products,  of  which  urea  is  the  chief.  The 
constant  katabolism,  on  the  other  hand,  is  largely  repre- 
sented by  creatinin  and  to  a  lesser  degree  by  uric  acid.  The 
more  the  total  katabolism  is  reduced,  the  more  prominent 
become  creatinin  and  uric  acid,  products  of  the  constant 
katabolism ;  while  urea,  as  chief  representative  of  the  variable 
katabolism,  becomes  less  conspicuous.  Folin  suggests  the 
term  endogenous  or  tissue  metabolism  for  the  constant  variety, 
while  the  variable  form  he  would  name  exogenous  or  interme- 
diate metabolism. 

In  these  suggestions  we  have  not  theory  only,  but  a 
number  of  very  important  facts  which  plainly  must  have 
some  significance.  Take,  for  example,  the  excretion  of 

10 


146  THE  NUTRITION  OF  MAN 

creatinin.  It  is  a  characteristic  nitrogenous  waste  product, 
but  its  elimination  from  the  body  is  wholly  independent 
of  quantitative  changes  in  the  total  amount  of  nitrogen 
excreted.  In  other  words,  the  amount  of  creatinin  elim- 
inated is  a  constant  quantity  for  a  given  individual  under 
ordinary  conditions,  no  matter  how  great  the  variation  in  the 
amount  of  proteid  food,  provided  no  meat  is  eaten.  Meat 
must  be  avoided  in  testing  this  point,  since  meat  contains  a 
certain  amount  of  creatin,  or  other  components,  which  would 
be  excreted  as  creatinin.  Further,  it  is  found  that  every  in- 
dividual has  his  own  specific  creatinin  excretion,  which  fact 
again  emphasizes  the  idea  that  this  substance  is  a  product  of 
true  tissue  katabolism,  having  no  connection  with  that  vari- 
able metabolism,  of  which  urea  is  the  striking  representative. 
These  are  facts  which  cannot  be  ignored.  They  are  well 
established  by  the  careful  observations  of  Folin,  and  they  are 
confirmed  by  a  large  number  of  observations  made  in  our 
own  laboratory.  Turn  now  to  that  other,  more  conspicuous, 
product  of  proteid  katabolism,  urea.  With  a  so-called  aver- 
age proteid  intake,  about  88-90  per  cent  of  the  excreted 
nitrogen  will  be  in  the  form  of  urea,  but,  as  Folin  states, 
"with  every  decided  diminution  in  the  quantity  of  total 
nitrogen  eliminated,  there  is  a  pronounced  reduction  in  the 
per  cent  of  that  nitrogen  represented  by  urea.  When  the 
daily  total  nitrogen  elimination  has  been  reduced  to  3  grams 
or  4  grams,  about  60  per  cent  of  it  only  is  in  the  form  of 
urea."  Here,  we  have  the  chief  product  of  exogenous  metab- 
olism, a  substance  quite  distinct  from  creatinin,  just  as  the 
process  by  which  it  originates  is  likewise  quite  distinct. 

Exogenous  metabolism  is  plainly  a  process  of  quite  a  differ- 
ent order  from  that  of  endogenous,  or  tissue  metabolism. 
The  latter  involves  oxidation,  while  the  former  consists  essen- 
tially of  a  series  of  hydrolytic  cleavages  which  result  in  a 
rapid  elimination  of  the  proteid-nitrogen  as  urea.  In  this 


THEORIES  OF  PROTEID  METABOLISM         147 

conception  of  exogenous  katabolism,  we  have  essentially  the 
same  viewpoint  as  was  previously  taken  in  attempting  to 
explain  how  excess  of  proteid  food  can  be  so  quickly  decom- 
posed, and  its  nitrogen  removed  from  the  body.  Whether 
the  hydrolytic  cleavage  is  accomplished  solely  by  trypsin  and 
erepsin,  whether  it  takes  place  only  in  the  intestine  and  in  the 
liver,  or  whether  other  glands  and  tissues  are  involved,  is  at 
present  immaterial ;  the  essential  point  is  that  we  have  in  the 
body  a  variety  of  proteid  katabolism,  quite  different  from  true 
tissue  katabolism,  the  extent  of  which  is  dependent  primarily 
upon  the  amount  of  proteid  food  consumed.  The  process  in- 
volved is  one  which  aims  at  the  rapid  removal  of  the  proteid- 
nitrogen  as  urea;  without  incorporation  of  the  absorbed 
proteid,  or  its  decomposition  products,  either  as  an  integral 
or  adherent  part  of  the  tissue  proteid.  Hydrolytic  cleavage 
is  eminently  fitted  to  accomplish  this  with  the  least  expendi- 
ture of  energy,  while  the  carbonaceous  residue  of  the  proteid 
thus  freed  from  nitrogen  can  be  transformed  into  carbohy- 
drate, or  directly  oxidized  as  the  needs  of  the  body  demand. 

As  one  considers  these  views  so  admirably  worked  out  by 
Folin,  the  question  naturally  arises,  if  the  real  demands  of 
the  body  for  proteid  food  will  not  be  adequately  met  by  the 
quantity  necessary  to  satisfy  the  true  tissue  metabolism? 
We  may  well  believe,  with  Folin,  that  "  only  a  small  amount 
of  proteid,  namely,  that  necessary  for  the  endogenous  metab- 
olism, is  needed.  The  greater  part  of  the  proteid  furnished 
with  so-called  standard  diets,  like  Voit's,  i.  e.,  that  part  rep- 
resenting the  exogenous  metabolism,  is  not  needed;  or,  to 
be  more  specific,  its  nitrogen  is  not  needed.  The  organism 
has  developed  special  facilities  for  getting  rid  of  such  excess  of 
nitrogen,  so  as  to  get  the  use  of  the  carbonaceous  part  of  the 
proteid  containing  it."  In  endogenous  metabolism,  we  have 
a  steady,  constant  process  quite  independent  of  the  amount 
of  proteid  food,  and  absolutely  indispensable  for  the  main- 


148  THE  NUTRITION  OF  MAN 

tenance  of  life.  So  far  as  we  know  at  present,  its  representa- 
tive creatinin  is,  for  a  given  individual,  the  same  in  amount 
during  fasting  as  when  a  rich,  meat-free,  proteid  diet  is  taken. 
The  one  factor  that  seemingly  determines  the  amount  of 
creatinin  eliminated  is  the  weight  of  the  individual,  or  more 
exactly  the  weight  of  the  true  tissue  elements  of  the  body,  as 
distinct  from  fat  or  adipose  tissue.  Endogenous  or  tissue 
katabolism  obviously  calls  for  a  certain  quantity  of  proteid 
to  maintain  equilibrium,  but  this  is  small  in  amount  as  com- 
pared with  the  usual  intake  of  proteid  foods.  The  average 
man,  with  his  ordinary  dietetic  habits,  consumes  more  nitro- 
gen than  the  body  can  possibly  make  use  of.  The  excess  is 
not  stored  up,  "  because  the  actual  need  of  nitrogen  is  so  small 
that  an  excess  is  always  furnished  with  the  food,  except,  of 
course,  in  carefully  planned  experiments  "  (Folin). 

We  have  seen  at  what  low  levels  of  proteid  intake,  nitrogen 
equilibrium  can  be  established,  and  we  may  well  have  faith 
in  the  conception  of  an  endogenous  proteid  katabolism  which 
involves  only  minimal  quantities  of  proteid.  Further,  we 
have  observed  the  constant  tendency  of  the  body  to  maintain 
a  condition  of  nitrogenous  equilibrium,  even  with  varying 
income,  and  how  slow  the  body  is  to  lay  by  nitrogen  on  a 
rich  proteid  diet,  even  when  long  deprived  of  proteid  food ; 
a  fact  difficult  of  explanation  except  on  the  assumption  that 
the  real  need  of  the  body  for  nitrogen  is  small,  and  that  the 
tissues  habitually  carry  a  relatively  large  reserve  of  nitroge- 
nous material.  We  may  assume  with  Folin  that  "  all  the  liv- 
ing protoplasm  in  the  animal  organism  is  suspended  in  a  fluid 
very  rich  in  proteid,  and  on  account  of  the  habitual  use  of 
more  nitrogenous  food  than  the  tissues  can  use  as  proteid  the 
organism  is  ordinarily  in  possession  of  approximately  the 
maximum  amount  of  reserved  proteid  in  solution  that  it  can 
advantageously  retain.  When  the  supply  of  food  proteid  is 
stopped,  the  excess  of  reserve  proteid  inside  the  organism  is 


THEORIES  OF  PROTEID  METABOLISM         149 

still  sufficient  to  cause  a  rather  large  destruction  of  proteid 
during  the  first  day  or  two  of  proteid  starvation,  and  after  that 
the  proteid  katabolism  is  very  small,  provided  sufficient  non- 
nitrogenous  food  is  available.  But  even  then,  and  for  many 
days  thereafter,  the  protoplasm  of  the  tissues  has  still  an 
abundant  supply  of  dissolved  proteid,  and  the  normal  activ- 
ity of  such  tissues  as  the  muscles  is  not  at  all  impaired  or 
diminished.  When  30  grams  or  40  grams  of  nitrogen  have 
been  lost  by  an  average-sized  man  during  a  week  or  more  of 
abstinence  from  nitrogenous  food  the  living  muscle  tissues 
are  still  well  supplied  with  all  the  proteid  they  can  use. 
That  this  is  so,  is  indicated  on  the  one  hand  by  the  un- 
changed creatinin  elimination,  and  on  the  other  by  the  fact 
that  one  experiences  no  feeling  of.  unusual  fatigue  or  of  in- 
ability to  do  one's  customary  work.  Because  the  organism 
at  the  end  of  such  an  experiment  still  has  an  abundance  of 
available  proteid  in  the  nutritive  fluids,  it  is  at  once  seem- 
ingly wasteful  with  nitrogen  when  a  return  is  made  to  nitrog- 
enous food.  This  is  why  it  only  gradually,  and  only  under 
the  prolonged  pressure  of  an  excessive  supply  of  food-proteid 
again  acquires  its  original  maximum  store  of  this  reserve 
material." 

We  may  reasonably  suppose  that  the  reserve  of  proteid 
present  in  the  body  is  contained  in  the  fluid  media,  and  not 
as  a  part  of  the  living  protoplasm.  Further,  we  are  appar- 
ently justified  in  the  belief  that  the  sole  form  of  proteid 
katabolism  which  is  vitally  important  for  the  welfare  of  the 
body  is  the  endogenous  katabolism.  This  must  be  provided 
for  adequately  and  indeed  liberally,  and  in  addition  there 
should  be  sufficient  intake  to  keep  up  an  abundant  supply  of 
reserve  proteid,  but  beyond  these  necessities  there  would 
seem  to  be  no  legitimate  demand  for  additional  proteid.  The 
voluminous  exogenous  proteid  katabolism  so  conspicuous  in 
most  individuals  would  seem  to  have  no  justification  in  fact, 


150  THE  NUTEITION   OF  MAN 

or  in  physiological  reasoning.  What  good,  for  example,  can 
be  accomplished  by  this  constant  splitting  off  of  nitrogen, 
with  its  subsequent  speedy  removal  from  the  body?  The 
organism  can  neither  use  it  nor  store  it  up,  and  why  there- 
fore should  this  daily  burden  of  an  excessive  and  accelerated 
proteid  katabolism  be  borne  ?  As  we  have  seen,  the  energy 
of  muscle  work  is  derived  mainly,  and  can  come  wholly,  from 
the  breaking  down  of  non-nitrogenous  materials,  fats  and 
carbohydrates.  The  very  fact  that  an  intake  of  say  120 
grams  of  proteid  is  followed  at  once  by  the  removal  of  the 
larger  part  of  the  contained  nitrogen,  as  a  result  of  the  ex- 
ogenous katabolism  of  the  body,  would  seemingly  warrant 
the  view  that  the  proteid  so  decomposed  might  advantageously 
be  replaced  by  a  corresponding  amount  of  carbohydrate.  In 
muscle  work,  as  in  heat  production,  carbohydrate  and  fat  are 
the  materials  burned  up,  or  oxidized.  Proteid,  on  the  other 
hand,  is  not  so  oxidized,  at  least  not  the  nitrogen-containing 
portion  of  the  molecule. 

There  are  apparent  only  two  possible  reasons  for  assum- 
ing a  need  on  the  part  of  the  body  for  the  high  exogenous 
katabolism  of  proteid  so  commonly  observed.  The  one  is 
that  the  carbonaceous  residue  left  after  the  cleavage  of  ni- 
trogen from  the  proteid  molecule  is  better  adapted  for  the 
needs  of  the  body  than  either  carbohydrate  or  fat.  Although 
this  does  not  seem  very  probable,  it  is  of  course  a  possibility 
and  merits  consideration.  Feeding  experiments,  with  a  com- 
paratively small  proteid  intake,  continued  over  a  sufficient 
length  of  time,  would  show  conclusively  how  much  weight 
should  be  attached  to  this  hypothesis.  The  other  possibility 
is  that  the  body  may  derive  some  advantage  from  the  pres- 
ence, in  the  tissues  and  fluids,  of  the  varied  nitrogenous 
cleavage  products  split  off  from  proteid  so  abundantly  in 
exogenous  katabolism.  These  substances  are  mainly  amino- 
acids  on  their  way  to  urea,  and  there  is  no  apparent  reason 


THEORIES   OF  PKOTEID   METABOLISM         151 

why  they  should  be  of  service  to  the  organism.  Still,  the 
processes  going  on  in  the  tissues  and  organs  of  the  body  are 
intricate  and  not  wholly  understood,  and  we  can  conceive  of 
some  useful  function  of  which  as  yet  we  have  no  knowledge. 
In  the  construction  of  tissue  proteid,  for  example,  as  in  a 
possible  synthesis  out  of  the  fragments  formed  by  hydrolytic 
cleavage,  it  is  not  impossible  that  certain  corner-stones  are 
needed,  and  that  in  order  to  obtain  these  there  must  be 
a  more  or  less  wasteful  breaking  down  of  food-proteid. 
However  improbable  this  may  seem,  it,  like  the  preceding 
hypothesis,  can  be  tested  in  a  way  by  adequate  feeding  ex- 
periments, which  shall  determine  the  effect  on  the  body 
of  a  low  proteid  intake  continued  over  a  long  period  of  time. 
On  the  other  hand,  it  is  equally  plausible,  and  for  some 
reasons  more  probable,  to  assume  that  this  excessive  exog- 
enous katabolism  may  be  in  a  measure  prejudicial  to  the 
best  interests  of  the  body;  that  the  many  nitrogenous  frag- 
ments formed  in  the  efforts  of  the  organism  to  prevent 
undue  accumulation  of  reserve  proteid  may  in  the  long  run 
do  as  much  harm  as  good. 

Further,  there  is  reason  in  the  question  whether  the  con- 
tinual carrying  of  excessive  amounts  of  nitrogen  reserves  in 
the  shape  of  soluble  proteid  in  the  blood  and  lymph,  and  in 
the  meshes  of  tissue  and  cell  protoplasm,  is  advantageous  for 
the  maintenance  of  the  highest  degree  of  efficiency?  We  all 
recognize  that  an  excessive  accumulation  of  fat  is  distinctly 
disadvantageous  to  the  welfare  of  the  body,  and  there  is, 
physiologically  speaking,  equally  good  ground  for  considering 
that  the  storage  of  unorganized  proteid  in  amounts  beyond 
all  possible  requirements  of  the  body  may  be  equally  un- 
desirable. Because  less  tangible  to  the  eye,  the  accumula- 
tion of  unnecessary  proteid  is  not  so  easily  recognizable,  but 
this  fact  does  not  diminish  the  possible  danger  which  such 
accumulation  may  constitute.  It  must  be  granted,  however. 


152  THE  NUTRITION  OF  MAN 

that  we  are  dealing  here  with  hypotheses  and  not  facts,  but 
though  hypothetical  the  suggestions  made  are  of  sufficient 
moment  to  merit  attention  and  experimental  study.  In  a 
later  chapter,  we  shall  have  occasion  to  present  some  facts 
bearing  on  these  questions. 

In  the  meantime,  we  may  lay  due  stress  upon  the  signif- 
icance of  these  views  regarding  proteid  katabolism.  We 
must  accept  as  settled  the  general  idea  that  there  are  two 
distinct  forms  of  proteid  katabolism  within  the  body;  one 
form  representing  the  decay  of  tissue  or  cell  protoplasm, 
small  in  amount,  with  its  own  particular  decomposition  prod- 
ucts, and  absolutely  essential  for  the  continuance  of  life. 
The  other  form,  the  so-called  exogenous  katabolism,  runs  a 
totally  different  course  with  distinctive  side-products  and 
end-products;  it  is  variable  in  extent,  in  harmony  with 
variations  in  proteid  intake,  and  subject  to  the  suspicion 
that  at  the  level  ordinarily  maintained  it  constitutes  a  menace 
to  the  preservation  of  that  high  degree  of  efficiency  which 
is  an  attribute  of  good  health. 


CHAPTER  V 

DIETARY  HABITS  AND  TRUE  FOOD  REQUIREMENTS 

TOPICS  :  Dietetic  customs  of  mankind.  Origin  of  dietary  standards. 
True  food  requirements.  Arguments  based  on  custom  and  habit. 
Relationship  between  food  consumption  and  prosperity.  Erroneous 
ideas  regarding  nutrition.  Commercial  success  and  national  wealth 
not  the  result  of  liberal  dietary  habits.  Instinct  and  craving  not  wise 
guides  to  follow  in  choice  and  quantity  of  food.  Physiological  re- 
quirements and  dietary  standards  not  to  be  based  on  habits  and  crav- 
ings. Old-time  views  regarding  temperate  use  of  food.  The  sayings 
of  Thomas  Cogan.  The  teachings  of  Cornaro.  Experimental  results 
obtained  by  various  physiologists.  Work  of  the  writer  on  true  proteid 
requirements.  Studies  with  professional  men.  Nitrogen  equilibrium 
with  small  amounts  of  food.  Sample  dietaries.  Simplicity  in  diet. 
Nitrogen  requirement  per  kilogram  of  body-weight.  Fuel  value  of 
the  daily  food.  Experiments  with  university  athletes.  Nitrogen 
balance  and  food  consumption.  Sample  dietaries.  Adequacy  of  a 
simple  diet. 

HAVING  acquired  information  regarding  the  principles 
of  metabolism  and  the  general  laws  governing  the 
nutrition  of  the  body,  we  may  next  consider  briefly  the 
dietetic  habits  of  mankind,  with  a  view  to  learning  how 
far  such  habits  coincide  with  actual  nutritive  requirements. 
Eventually,  we  shall  need  to  ask  the  questions :  What  are  the 
true  nutritive  requirements  .of  the  body  ?  How  much  food 
and  what  kinds  of  food  does  the  ordinary  individual  doing 
an  average  amount  of  work  need  each  day  in  order  to  pre- 
serve body  equilibrium,  and  to  maintain  health,  strength,  and 
vigor  under  the  varying  conditions  of  life?  What  amount 
of  nitrogen  or  proteid,  and  what  the  total  calorific  value 


154  THE  NUTRITION  OF  MAN 

required  to  supply  the  physiological  needs  of  the  body? 
How  closely  do  the  so-called  "normal  diets  "  and  "standard 
diets,"  which  have  met  with  such  general  acceptance,  con- 
form to  a  rational  conception  of  true  physiological  needs? 
These  are  vital  questions  of  great  physiological  and  economic 
importance,  and  they  are  not  easily  answered;  but  theoret- 
ical considerations  based  on  scientific  data,  and  experimental 
evidence  combined  with  practical  experience,  should  point 
the  way  to  some  very  definite  conclusions. 

Observations  made  in  many  countries  regarding  the  dietetic 
customs  and  habits  of  the  people  have  resulted  in  the  estab- 
lishment of  certain  dietary  standards,  which  have  been  more 
or  less  generally  adopted  as  representing  the  requirements  of 
the  body.  As  a  prelude  to  the  discussion  of  this  question, 
let  us  consider  briefly  some  of  the  results  of  these  dietary 
studies.  In  Sweden,  laborers  doing  hard  work  were  found 
by  Hultgren  and  Landergren  to  consume  daily,  on  an  aver- 
age, 189  grams  of  proteid,  714  grams  of  carbohydrate,  and 
110  grams  of  fat,  with  a  total  fuel  value  for  the  day's  ration 
of  4726  large  calories.  In  Russia,  workmen  at  moderately 
hard  labor,  having  perfect  freedom  of  choice  in  their  food, 
were  found  by  Erisman  to  take  daily  132  grams  of  proteid, 
584  grams  of  carbohydrate,  and  79  grams  of  fat,  this  ration 
having  a  fuel  value  of  3675  calories.  In  Germany,  soldiers 
in  active  service  consumed  daily,  according  to  Voit,  145 
grams  of  proteid,  500  grams  of  carbohydrate,  and  100  grams 
of  fat,  with  a  fuel  value  of  3574  calories.  In  Italy,  laborers 
doing  a  moderate  amount  of  work  were  found  by  Lichtenfelt 
to  consume  daily  115  grams  of  proteid,  696  grams  of  carbohy- 
drate, and  26  grams  of  fat,  with  a  fuel  value  of  3655  calories. 
In  France,  Gautier  states  that  the  ordinary  laborer  working 
eight  hours  a  day  must  have  135  grams  of  proteid,  700  grams 
of  carbohydrate,  and  90  grams  of  fat  daily,  with  a  fuel  value 
of  4260  calories.  In  England,  weavers  were  found  to  take 


DIETAEY  HABITS 


155 


daily  151  grams  of  proteid,  with  carbohydrates  and  fats  suffi- 
cient to  make  the  total  fuel  value  of  the  day's  ration  equal 
to  3475  calories.  In  Austria,  farm  laborers  consumed  daily 
159  grams  of  proteid,  with  carbohydrates  and  fats  sufficient 
to  raise  the  fuel  value  of  the  food  to  5096  calories. 

Observations  of  this  order  might  be  multiplied  indefinitely, 
but  the  above  will  suffice  to  give  a  general  idea  of  the  aver- 
age food  consumption  of  European  peoples  doing  a  moderate 
amount  of  work.  These  data,  however,  must  be  supplemented 
by  the  observations  made  in  our  own  country,  which  have  been 
very  extensive,  through  the  "  investigations  on  the  nutrition 


Subjects. 

Proteid  consumed 
Daily. 

Total  Fuel  Value 
of  Daily  Food. 

Swedish  laborers,  at  hard  work    .... 

grams 
189 

calories 

4726 

Russian  workmen,  moderate  work  .     .     . 

132 

3675 

German  soldiers,  active  service    .... 

145 

3574 

Italian  laborers,  moderate  work  .... 

115 

3655 

French  laborers,  eight  hours'  work  .     .     . 

135 
151 

4260 
3475 

Austrian  farm  laborers    

159 

5096 

American  Subjects. 

Man  with  very  hard  muscular  work     .     . 

175 

5500 

Man  with  hard  muscular  work     .... 

150 

4150 

Man   with    moderately  active    muscular 
work 

125 

3400 

Man    with   light    to   moderate   muscular 
work  ....         

112 

3050 

Man  at  "sedentary  "  or  woman  with  mod- 
erately active  work 

100 

2700 

of  man  in  the  United  States,"  carried  on  by  the  Office  of  Ex- 
periment Stations  in  the  Department  of  Agriculture,  under 
the  efficient  leadership  of  Atwater.  As  stated  by  Messrs. 


156  THE  NUTRITION  OF  MAN 

Langworthy  and  Milner,  in  an  official  bulletin  issued  in  1904, 
dietary  studies  of  the  actual  food  consumption  of  people  of 
different  classes  in  different  parts  of  the  United  States  have 
been  made  during  the  years  1894  to  1904  on  about  15,000 
persons,  —  men,  women,  and  children,  —  as  a  result  of  which 
it  is  indicated  that  "  the  actual  food  requirements  of  persons 
under  different  conditions  of  life  and  work  "  vary  from  100 
to  175  grams  of  proteid  per  day,  with  a  total  fuel  value  rang- 
ing from  2700  to  5500  calories.  For  comparison,  the  various 
data  may  be  tabulated  as  shown  on  page  155. 

These  figures  by  no  means  represent  maximum  food  con- 
sumption. Thus,  studies  have  been  made  on  fifty  Maine 
lumbermen,1  where  the  intake  of  proteid  food  averaged  185 
grams  per  day,  with  a  total  fuel  value  of  6400  calories. 
Further,  dietary  studies  of  university  boat  crews  2  have  shown 
fairly  high  results.  The  Yale  University  crew,  while  at 
Gales  Ferry,  averaged  per  man  during  seven  days  171  grams 
of  proteid,  171  grams  of  fat,  and  434  grams  of  carbohydrate, 
with  a  total  fuel  value  of  4070  calories  per  day.  The  mem- 
bers of  the  Harvard  University  crew  showed  an  average 
daily  consumption  of  160  grams  of  proteid,  170  grams  of 
fat,  and  448  grams  of  carbohydrate,  with  a  total  fuel  value 
of  4074  calories.  It  is  also  reported  that  a  football  team  of 
college  students  in  the  University  of  California  consumed 
daily,  per  man,  270  grams  of  proteid,  416  grams  of  fat,  and 
710  grams  of  carbohydrate,  with  a  total  fuel  value  of  7885 
calories.  These  figures  may  be  contrasted,  however,  with  the 
data  obtained  in  a  study  of  the  dietary  habits  of  fourteen  pro- 
fessional men's  families,  where  the  average  amount  of  proteid 
consumed  daily  was  104  grams,  fat  125  grams,  and  carbohy- 
drate 423  grams,  with  a  total  fuel  value  of  3325  calories. 

1  Bulletin  No.  149.     Woods  and  Mansfield.     Studies  of  the  Food  of  Maine 
Lumberme-.     U.  S.  Department  of  Agriculture,  1904. 

2  Bulletin  No.  75.    Atwater  and  Bryant.    Office  of  Experiment  Stations, 
TJ.  S.  Department  of  Agriculture,  1900 


DIETAKY  HABITS  157 

Leaving  out  of  consideration  the  extremes  given,  it  is 
undoubtedly  true  that,  within  certain  rather  wide  limits, 
there  is  an  apparent  tendency  for  people  of  different  nations, 
having  a  free  choice  of  food  and  not  restricted  by  expense, 
to  consume  daily  approximately  the  same  amounts  of  nutri- 
ents; to  use  what  may  be  called  liberal  rather  than  small 
amounts  of  food;  and,  lastly,  to  consume  food  somewhat  in 
proportion  to  the  amount  of  work  done.  It  is  perhaps,  there- 
fore, not  strange  that  students  of  nutrition  should  have  taken 
these  results,  obtained  by  the  statistical  method,  as  indicat- 
ing the  actual  needs  of  the  body  for  food,  and  that  so-called 
"standard  diets"  and  "normal  diets"  should  have  been  con- 
structed, based  upon  these  and  corresponding  data.  Thus, 
we  have  the  widely  adopted  "  Voit  standard,"  composed  of 
proteid  118  grams,  carbohydrate  500  grams,  and  fat  56 
grams,  with  a  total  fuel  value  of  3055  calories,  as  the  amount 
of  food  required  daily  by  a  man  of  70  kilos  body-weight 
doing  a  moderate  amount  of  work.  These  figures  were  ob- 
tained by  Voit  as  an  average  of  the  food  consumption  of  a 
large  number  of  laboring  men  in  Germany,  and  they  carried 
additional  weight  because  at  that  time  Voit  and  others 
thought  they  had  evidence  that  nitrogenous  equilibrium 
could  not  be  maintained  for  any  length  of  time  on  smaller 
amounts  of  proteid. 

The  figures  given  in 'the  preceding  table  under  the  head 
of  American  subjects  constitute  the  "Atwater  standards," 
and  as  already  indicated,  are  based  upon  the  dietetic  habits 
of  over  15,000  persons  under  different  conditions  of  life  and 
physical  activity.  In  the  words  of  the  official  Bulletin,  these 
standards  covering  the  quantities  of  food  per  day  "are  in- 
tended to  show  the  actual  food  requirements  of  persons 
under  different  conditions  of  life  and  work."  Here,  how- 
ever, lies  an  assumption  which  seems  to  meet  with  wide 
acceptance,  but  for  which  it  is  difficult  to  conceive  any 


158  THE  NUTEITION  OF  MAN 

logical  reason.  The  thousands  of  dietary  studies  made  on 
peoples  all  over  the  world,  affording  more  or  less  accurate 
information  regarding  the  average  amounts  of  proteid,  fat, 
and  carbohydrate  consumed  under  varying  conditions,  are  in- 
deed most  interesting  and  important,  as  affording  informa- 
tion regarding  dietetic  customs  and  habits;  but,  the  writer 
fails  to  see  any  reason  why  such  data  need  be  assumed 
to  throw  any  light  on  the  actual  food  requirements  of  the 
body.  In  the  words  of  another,  "  Food  should  be  ingested  in 
just  the  proper  amount  to  repair  the  waste  of  the  body;  to 
furnish  it  with  the  energy  it  needs  for  work  and  warmth; 
to  maintain  it  in  vigor;  and,  in  the  case  of  immature  animals, 
to  provide  the  proper  excess  for  normal  growth,  in  order  to 
be  of  the  most  advantage  to  the  body"  (Benedict). 

Any  habitual  excess  of  food,  over  and  above  what  is  really 
needed  to  meet  the  actual  wants  of  the  body,  is  not  only 
uneconomical,  but  may  be  distinctly  disadvantageous.  Voit, 
among  others,  has  clearly  emphasized  the  general  principle 
that  the  smallest  amount  of  proteid,  with  non-nitrogenous 
food  added,  that  will  suffice  to  keep  the  body  in  a  state  of 
continual  vigor  is  the  ideal  diet.  My  own  conception  of  the 
true  food  requirements  of  the  body  has  been  expressed  in  the 
statement  that  man  needs  of  proteids,  fats,  and  carbohydrates 
sufficient  to  establish  and  maintain  physiological  and  nitrogen 
equilibrium ;  sufficient  to  keep  up  that  strength  of  body  and 
mind  that  is  essential  to  good  health,  to  maintain  the  highest 
degree  of  physical  and  mental  activity  with  the  smallest 
amount  of  friction  and  the  least  expenditure  of  energy,  and 
to  preserve  and  heighten,  if  possible,  the  ordinary  resistance 
of  the  body  to  disease  germs.  The  smallest  amount  of  food 
that  will  accomplish  these  ends  is,  I  think,  the  ideal  diet. 
There  must  truly  be  enough  to  supply  the  real  needs  of  the 
body,  but  any  great  surplus  over  and  above  what  is  actually 
called  for  may  in  the  long  run  prove  an  undesirable  addition. 


DIETARY  HABITS  159 

With  these  thoughts  in  mind,  may  we  not  reasonably  ask 
why  it  should  be  assumed  that  there  is  any  tangible  connec- 
tion between  the  dietetic  habits  of  a  people  and  their  true 
physiological  needs? 

Arguments  predicated  on  custom,  habit,  and  usage  have 
no  physiological  basis  that  appeals  strongly  to  the  impartial 
observer.  Man  is  a  creature  of  habits ;  he  is  quick  to  acquire 
new  ones  when  his  environment  affords  the  opportunity,  and 
he  is  prone  to  cling  to  old  ones  when  they  minister  to  his 
sense  of  taste.  The  argument  that  because  the  people  of  a 
country,  constituting  a  given  class,  eat  a  certain  amount  of 
proteid  food  daily,  the  quantity  so  consumed  must  be  an 
indication  of  the  amount  needed  to  meet  the  requirements 
of  the  body,  is  as  faulty  as  the  argument  that  because  people 
of  a  given  community  are  in  the  habit  of  consuming  a  certain 
amount  of  wine  each  day  at  dinner  their  bodies  must  neces- 
sarily be  in  need  of  the  stimulant,  and  that  consequently 
alcohol  is  a  true  physiological  requirement.  A  large  propor- 
tion of  mankind  is  addicted  to  the  tobacco  habit,  and  to 
many  persons  the  after-dinner  cigar  is  as  essential  to  comfort 
as  the  dinner  itself ;  but  would  any  one  think  of  arguing  that 
tobacco  is  one  of  the  physiological  needs  of  the  body  ? 

It  is  said  that  dietary  studies  made  all  over  the  civilized 
world  "  show  that  a  moderately  liberal  quantity  of  protein  is 
demanded  by  communities  occupying  leading  positions  in  the 
world.  ...  It  certainly  seems  more  than  a  remarkable  coin- 
cidence that  peoples  varying  so  widely  in  regard  to  national- 
ity, climatic  and  geographical  conditions,  and  dietetic  habits, 
should  show  such  agreement  in  respect  to  consumption  of 
protein  and  energy."  Again,  we  hear  it  said  that  "what- 
ever may  be  true  of  a  few  individuals,  with  communities  a 
generally  low  condition  of  mental  and  physical  efficiency, 
thrift,  and  commercial  success,  is  coincident  with  a  low  pro- 
portion of  protein  in  the  diet."  The  writer,  however,  fails 


160  THE  NUTRITION   OF  MAN 

to  find  evidence  in  the  results  afforded  by  dietary  studies 
that  there  is  any  causal  relationship  between  the  amount  of 
proteid  food  consumed  and  the  mental  or  physical  supremacy 
of  the  people  of  a  given  nation  or  community.  Cause  and 
effect  are  liable  to  become  reversed  in  arguments  of  this 
kind.  It  is  certainly  just  as  plausible  to  assume  that  in- 
crease in  the  consumption  of  proteid  follows  in  the  footsteps 
of  commercial  and  other  forms  of  prosperity,  as  to  argue 
that  prosperity  or  mental  and  physical  development  are  the 
result  of  an  increased  intake  of  proteid  food. 

Proteid  foods  are  usually  costly,  and  the  ability  of  a  com- 
munity to  indulge  freely  in  this  form  of  dietetic  luxury 
depends  in  large  measure  upon  its  commercial  prosperity. 
The  palate  is  an  extremely  sensitive  organ,  and  the  average 
individual  properly  derives  great  satisfaction  from  the  pleas- 
urable effects  of  tasty  articles  of  food.  Furthermore,  there 
are  many  curious  and  quite  unphysiological  notions  abroad 
regarding  foods,  which  tend  to  incite  persons  to  unnecessary 
excess  and  extravagance  whenever  they  acquire  the  means 
to  do  so.  The  latter  point  is  well  illustrated  by  the  more 
or  less  prevalent  opinion  that  a  cut  of  tenderloin  steak  is 
more  nutritious  than  a  cut  of  round  steak.  It  is  true  that 
the  former  is  apt  to  be  more  tender,  to  have  a  little  finer 
flavor;  but  the  round  steak,  when  properly  prepared,  is  just 
as  nutritious,  and  equally  capable  of  meeting  the  needs  of 
the  body,  as  the  more  expensive  tenderloin.  With  increas- 
ing prosperity,  we  turn  at  once,  as  a  rule,  to  the  more  tasty 
and  appetizing  viands,  partly  to  satisfy  the  craving  of  appe- 
tite and  palate,  and  partly  because  there  is  an  inherenf  belief 
that  these  varied  delicacies,  accessible  to  the  prosperous  com- 
munity, count  as  an  aid  to  health  and  strength.  The  poor 
laborer,  with  his  small  wage,  is  restricted  to  a  certain  low 
level  of  dietary  variety,  and  must  likewise  be  economical  as 
to  quantity,  but  on  the  first  opportunity  afforded  by  a  fuller 


DIETAKY  HABITS  161 

purse  he  is  apt  to  pass  from  corned  beef  to  a  fresh  roast  with 
its  more  appetizing  flavor;  to  eschew  brown  bread  in  favor  of 
the  white  loaf,  and  in  many  other  ways  to  evince  his  desire 
for  a  dietary  which,  though  perhaps  no  more  nutritious,  ap- 
peals because  of  its  finer  flavor,  more  appetizing  appearance, 
and  greater  variety.  He  is  in  the  same  position  as  the 
smoker  who,  limited  by  his  purse  to  a  five -cent  cigar  after 
dinner,  quickly  passes  to  a  cigar  of  better  flavor  as  soon  as 
his  finances  warrant  the  indulgence.  At  the  same  time,  if 
prosperity  continues,  our  laborer  will  speedily  pass  to  a 
higher  level  of  proteid  intake  and  greater  fuel  value,  through 
increased  consumption  of  meat  and  butter,  together  with 
other  articles  rich  in  proteid  and  fat. 

In  this  connection,  we  may  emphasize  a  fact  of  some 
significance  in  its  bearing  on  dietetic  customs;  viz.,  that 
ever  since  Liebig  advanced  his  theory  that  proteid  material 
is  the  sole  source  of  muscular  energy,  there  has  been  a  deep- 
rooted  belief  that  meat  is  the  most  efficient  kind  of  food  for 
keeping  up  the  strength  of  the  body,  and  hence  especially 
demanded  by  all  whose  work  is  mainly  physical.  Although 
this  view,  as  we  have  seen,  has  been  thoroughly  disproved, 
the  idea  is  still  more  or  less  generally  held  that  an  abun- 
dance of  meat  is  a  necessary  requisite  for  a  good  day's  work, 
a  view  which  undoubtedly  accounts  in  some  measure  for  the 
tendency  toward  a  high  proteid  intake,  evinced  by  many  of 
the  laboring  class  whose  means  will  permit  the  necessary 
outlay. 

Increased  consumption  of  proteid  food  may  be  coincident 
with  thrift  and  commercial  success,  but  there  is  no  justifica- 
tion for  the  belief  that  these  are  the  result  of  changed  dietary 
conditions.  The  dietary  of  our  New  England  forefathers 
was,  according  to  all  accounts,  exceedingly  limited  as  com- 
pared with  that  of  to-day,  but  it  is  doubtful  if  the  present 
generation  is  any  better  developed,  physically  or  mentally, 

11 


162  THE  NUTRITION  OF  MAN 

than  the  stalwart  and  vigorous  people  who  opened  up  this 
country  to  civilization.  To-day,  as  a  nation,  we  have 
greater  wealth,  and  our  commercial  prosperity  has  become 
phenomenal;  but  would  any  one  think  for  a  moment  that 
these  characteristics  are  attributable  to  the  large  consump- 
tion of  proteid  food  so  common  to  this  generation  of  the 
American  people?  No,  increased  wealth  simply  paves  the 
way  for  greater  freedom  in  the  choice  of  food ;  increased  com- 
mercial success  and  business  prosperity  throw  open  avenues 
which  formerly  were  closed ;  greater  variety  of  animal  foods, 
and  vegetable  foods  as  well,  rich  in  proteid,  are  made  easily 
accessible,  and  appeal  to  eye  and  palate  on  all  sides;  appetite 
and  craving  for  food  are  abnormally  stimulated,  and  dietetic 
habits  and  customs  change  accordingly.  In  the  words  of 
another,  "the  one  thing  that  primitive,  barbarous,  and  civil- 
ized man  alike  long  for  is  an  abundance  of  the  '  flesh-pots  of 
Egypt.'  The  very  first  use  the  latter  makes  of  his  increased 
power  and  financial  resources  is  to  buy  new,  rare,  and  expen- 
sive kinds  of  meat."  With  these  facts  before  us,  it  is  difficult 
to  accept  the  assumption  that  dietetic  customs  afford  any 
indication  of  the  food  requirements  of  the  body.  To  the 
physiologist  such  a  view  does  not  appeal,  since  there  is  a 
lack  of  any  scientific  evidence  that  carries  conviction. 

But  it  may  be  asked,  is  not  appetite  a  safe  guide  to  follow  ? 
Do  not  the  cravings  of  the  stomach  and  the  so-called  pangs 
of  hunger  merit  consideration  ?  Is  it  not  the  part  of  wisdom 
to  follow  inclination  in  the  choice  and  quantity  of  our  food  ? 
Can  we  not  safely  rely  upon  these  factors  as  an  index  of 
the  real  needs  of  the  body?  If  these  questions  are  to  be 
answered  in  the  affirmative,  then  it  is  plain  that  a  study  of 
dietetic  customs  will  tell  us  definitely  how  much  food  and 
what  kinds  of  food  are  required  daily  to  supply  the  true 
wants  of  the  body.  There  are  writers  who  claim  that  instinct 
is  a  perfectly  safe  guide  to  follow ;  that  it  is  far  superior  to 


DIETARY  HABITS  163 

reason ;  but  it  is  to  be  noticed  that  most  of  these  writers,  if 
they  have  any  physiological  knowledge  to  draw  upon,  are 
sooner  or  later  prone  to  admit  that  the  body  has  certain  defi- 
nite needs  which  it  is  the  purpose  of  food  to  supply,  with 
the  added  implication  that  any  surplus  of  food  over  and 
above  what  is  necessary  to  meet  these  demands  is  entirely 
uncalled  for.  Thus,  one  such  writer  states  that  "  the  man  in 
the  street  follows  his  God-given  instincts  and  plods  peace- 
fully along  to  his  three  square  meals  a  day,  consisting  of 
anything  he  can  find  in  the  market,  and  just  as  much  of  it 
as  he  can  afford,  with  special  preference  for  rich  meats,  fats, 
and  sugars."  Yet  this  same  writer,  a  little  later,  emphasizes 
the  fact  that  "every  particle  of  the  energy  which  sparkles 
in  our  eyes,  which  moves  our  muscles,  which  warms  our  im- 
aginations, is  sunlight  cunningly  woven  into  our  food  by  the 
living  cell,  whether  vegetable  or  animal.  Every  movement, 
every  word,  every  thought,  every  aspiration  represents  the 
expenditure  of  precisely  so  much  energy  derived  from  food." 
Why,  then,  would  it  not  be  wise  to  ascertain  how  much 
energy  is  so  expended,  on  an  average,  during  the  day's  activity 
and  govern  the  intake  of  food  accordingly  ?  Why  not  apply 
an  intelligent  supervision  in  place  of  following  an  instinct 
which,  in  the  words  of  the  author  just  quoted,  leads  one  on 
to  consume  "  anything  he  can  find  in  the  market  and  just  as 
much  of  it  as  he  can  afford  "  ?  Truly,  if  dietetic  customs 
and  the  habits  of  mankind  are  the  results  of  instinct  work- 
ing in  this  fashion,  there  cannot  be  much  value  in  the  data 
obtained  by  observing  the  quantities  of  food  mankind  is  in 
the  habit  of  eating.  Dietary  standards  based  on  such  ob- 
servations must  be  open  to  the  suspicion  of  representing 
values  far  above  the  actual  needs  of  the  body. 

Habits  and  cravings  are  certainly  very  unreliable  indices 
of  true  physiological  requirements.  Man  is  constantly  ac- 
quiring new  habits,  and  these  in  time  become  second  nature, 


164  THE   NUTRITION   OF  MAN 

forcing  him  to  practise  that  which  he  has  become  accustomed 
to,  regardless  of  whether  it  is  beneficial  or  otherwise.  The 
celebrated  philosopher,  John  Locke,  in  his  essay  on  educa- 
tion, says:  "I  do  not  think  all  people's  appetites  are  alike 
.  .  .  but  this  I  think,  that  many  are  made  gourmands  and 
gluttons  by  custom,  that  were  not  so  by  nature;  and  I  see 
in  some  countries,  men  as  lusty  and  strong,  that  eat  but  two 
meals  a  day,  as  others  that  have  set  their  stomachs  by  a  con- 
stant usage,  like  Larums,  to  call  on  them  for  four  or  five." 
Again,  the  so-called  cravings  of  appetite  are  largely  artificial 
and  mainly  the  result  of  habit.  A  habit  once  acquired  and 
persistently  followed  soon  has  us  in  its  grasp,  and  then  any 
deviation  therefrom  is  very  apt  to  disturb  our  physiological 
equilibrium.  The  system  makes  complaint,  and  we  experi- 
ence a  craving,  it  may  be,  for  that  to  which  the  body  has  be- 
come accustomed.  There  has  thus  come  about  a  sentiment 
that  the  cravings  of  the  appetite  for  food  are  to  be  fully 
satisfied,  that  this  is  merely  obedience  to  nature's  laws.  In 
reality,  there  is  no  foundation  for  such  a  belief;  any  one  with 
a  little  persistence  can  change  his  or  her  habits  of  life, 
change  the  whole  order  of  cravings,  thereby  indicating  that 
the  latter  are  essentially  artificial,  and  that  they  have  no 
necessary  connection  with  the  welfare  or  needs  of  the  body. 
The  man  who  for  some  reason  deems  it  advisable  to  adopt 
two  meals  a  day  in  place  of  three  or  four,  at  first  experiences 
a  certain  amount  of  discomfort,  but  eventually  the  new 
habit  becomes  a  part  of  the  daily  routine,  and  the  man's 
life  moves  forward  as  before,  with  perfect  comfort  and  with- 
out a  suggestion  of  craving,  or  a  pang  of  hunger.  Dietetic 
requirements,  and  standard  dietaries,  are  not  to  be  founded 
upon  the  so-called  cravings  of  appetite  and  the  instinctive 
demands  for  food,  but  upon  reason  and  intelligence,  re- 
inforced by  definite  knowledge  of  the  real  necessities  of  the 
bodily  machinery. 


DIETAKY  HABITS  165 

The  standards  which  have  been  adopted  more  or  less  gen- 
erally throughout  the  civilized  world,  based  primarily  on  the 
assumption  that  man  instinctively  and  independently  selects 
a  diet  that  is  best  adapted  to  his  individual  needs,  are  open 
to  grave  suspicion.  The  view  that  the  average  food  consump- 
tion of  large  numbers  of  individuals  and  communities  must 
represent  the  true  nutritive  requirements  of  the  people  is 
equally  untenable.  Naturally,  there  is  general  recognition  of 
the  principle  that  food  requirements  are  necessarily  modified 
by  a  variety  of  circumstances,  such  as  age,  sex,  body-weight, 
bodily  activity,  etc.  It  is  obvious  that  the  man  of  140  pounds 
body-weight  needs  less  proteid  than  the  man  of  170  pounds, 
and  that  the  man  who  does  a  large  amount  of  physical  work 
demands  a  larger  calorific  value  in  his  daily  diet,  i.  e.,  more 
carbohydrate  and  fat,  than  the  sedentary  individual.  The 
growing  child,  in  proportion  to  his  body- weight,  plainly  needs 
more  proteid  for  the  upbuilding  of  tissue,  and  there  are  many 
conditions  of  disease  where  special  dietetic  treatment  is  un- 
doubtedly called  for.  Our  contention,  however,  and  one 
which  we  believe  to  be  perfectly  justifiable,  is  that  the  true 
food  requirements  of  the  body,  under  any  conditions,  cannot 
be  ascertained  with  any  degree  of  accuracy  by  observations  of 
what  people  are  in  the  habit  of  eating;  that  customs  and 
habits  are  not  a  safe  index  of  true  physiological  needs.  On 
the  contrary,  we  are  inclined  to  the  belief  that  direct  physio- 
logical experimentation,  covering  a  sufficient  length  of  time 
and  with  an  adequate  number  of  individuals,  will  prove  far 
more  efficient  in  affording  a  true  estimate  of  the  quality  and 
quantity  of  food  best  adapted  for  the  maintenance  of  good 
health,  strength,  and  vigor. 

Before  considering  these  latter  points,  it  is  interesting  to 
note,  in  passing,  that  during  the  last  four  centuries  many 
thoughtful  men  have  called  attention  to  the  apparent  exces- 
sive use  of  food.  There  seems  to  have  been  in  many  quarters 


166  THE  NUTRITION   OF  MAN 

a  more  or  less  prevalent  opinion  that  custom  and  habit  were 
leading  people  on  to  methods  of  living,  which  were  not  in 
accord  with  the  best  interests  of  the  community.  It  must  be 
remembered,  however,  that  arguments  of  this  kind,  even  fifty 
years  ago,  could  have  been  founded  only  on  general  observa- 
tion and  the  application  of  common  sense,  since  there  were 
then  no  sound  physiological  data  on  which  to  predicate  an 
opinion,  or  base  a  conclusion.  Still,  there  were  men  of 
authority  who  attempted  to  lay  before  the  people  a  proper 
conception  of  the  temperate  use  of  food.  We  have  not  the 
time  here  to  consider  many  of  these  pleas,  but  I  venture  to 
call  attention  to  the  somewhat  celebrated  book  published  by 
the  physician  Thomas  Cogan  in  1596,  under  the  title  "  The 
Haven  of  Health,"  and  dedicated  "to  the  right  honorable  and 
my  verie  good  lord,  Sir  Edward  Seymour,  Knight  and  Earl 
of  Hertford."  Under  the  subject  of  diet,  this  old-time  writer 
says :  "  The  second  thing  that  is  to  be  considered  of  meates  is 
the  quantitie,  which  ought  of  all  men  greatly  to  be  regarded, 
for  therein  lyeth  no  small  occasion  of  health  or  sickness,  of 
life  or  death.  For  as  want  of  meate  consumeth  the  very  sub- 
stance of  our  flesh,  so  doth  excesse  and  surfet  extinguish  and 
suffocate  naturall  heat  wherein  life  consisteth."  Again,  "  Use 
a  measure  in  eating,  that  thou  maist  live  long:  and  if  thou 
wilst  be  in  health,  then  hold  thine  hands.  But  the  greatest 
occasion  why  men  passe  the  measure  in  eating,  is  varitie  of 
meats  at  one  meale.  Which  fault  is  most  common  among 
us  in  England  farre  above  all  other  nations.  For  such  is  our 
custome  by  reason  of  plentie  (as  I  think)  that  they  which  be 
of  abilitie,  are  served  with  sundry  sortes  of  meate  at  one 
meale.  Yea  the  more  we  would  welcome  our  friends  the 
more  dishes  we  prepare.  And  when  we  are  well  satisfied 
with  one  dish  or  two,  then  come  other  more  delicate  and  pro- 
cureth  us  by  that  meanes,  to  eate  more  than  nature  doth  re- 
quire. Thus  varietie  bringeth  us  to  excesse,  and  sometimes 


DIETARY   HABITS  167 

to  surfet  also.  But  Phisicke  teacheth  us  to  faede  moderately 
upon  one  kinde  of  meate  only  at  one  meale,  or  at  leastwise 
not  upon  many  of  contrarie  natures.  .  .  .  This  disease,  (I 
mean  surfet)  is  verie  common:  for  common  is  that  saying 
and  most  true :  That  more  die  by  surfet  than  by  the  sword. 
And  as  Georgius  Pictorius  saith,  all  surfet  is  ill,  but  of  bread 
worst  of  all.  And  if  nature  be  so  strong  in  many,  and  they 
be  not  sicke  upon  a  full  gorge,  yet  they  are  drowsie  and 
heavie,  and  more  desirous  to  loyter  than  to  labor,  according 
to  that  old  maeter,  when  the  belly  is  full,  the  bones  would 
be  at  rest.  Yea  the  minde  and  wit  is  so  oppressed  and  over- 
whelmed with  excesse  that  it  lyeth  as  it  were  drowned  for 
a  time,  and  unable  to  use  his  force." 

Cogan  likewise  makes  some  interesting  statements  regard- 
ing the  effects  of  custom  on  the  consumption  of  proteid 
food,  especially  meats.  Quoting  further  from  this  author : 
"The  fourth  thing  that  is  to  be  considered  in  meats  is 
custome.  Which  is  of  such  force  in  man's  bodie  both  in 
sicknesse  and  in  health,  that  it  countervaileth  nature  itselfe, 
and  is  therefore  called  of  Galen  in  sundry  places,  an  other 
nature.  Whereof  he  giveth  a  notable  example,  where  he 
sheweth  that  an  olde  woman  of  Athens  used  a  long  time, 
to  eate  Hemlocke  (which  is  a  ranke  poison)  first  a  little 
quantitie,  and  afterwarde  more,  till  at  length  she  could  eate 
so  much  without  hurt  as  would  presently  poison  another. 
...  So  that  custome  in  processe  of  time  may  alter  nature." 
Finally,  we  may  quote  one  last  saying  of  Cogan's,  because 
of  the  good  sense  and  wisdom  displayed  in  the  sentiment, 
as  true  to-day  as  when  it  was  written  more  than  three 
hundred  years  ago :  "  Neither  is  it  good  for  any  man  that  is 
in  perfect  health,  to  observe  any  custome  in  dyet  precisely, 
as  Arnold  us  teacheth  upon  the  same  verses  in  these  wordes : 
Every  man  should  so  order  himselfe,  that  he  might  be  able 
to  suffer  heate  and  cold,  and  all  motions,  and  meats  neces- 


168  THE  NUTRITION  OF  MAN 

sary,  so  as  he  might  change  the  houres  of  sleeping  and  wak- 
ing, and  his  dwelling  and  lodging  without  harme:  which 
thing  may  be  done  if  we  be  not  too  precise  in  keeping  cus- 
tome,  but  otherwise  use  things  unwonted.  Which  sentence 
of  Arnoldus  agraeth  verie  well  to  that  of  Cornelius  Celsus : 
He  that  is  sound  and  in  good  health,  and  at  libertie,  should 
bind  himselfe  to  no  rules  of  dyet.  To  need  neither  Phisition 
or  Chirurgion,  he  must  use  a  diverse  order  of  life,  and  be 
sometimes  in  the  countrie,  sometime  in  the  towne,  sometimes 
hunt,  and  sometime  hawke.  But  some  man  may  demand  of 
me  how  this  may  agree  with  that  saying  of  the  scholar  of 
Salernus  '  if  you  would  be  free  from  physicians,  let  these 
three  be  your  physician,  a  cheerful  mind,  rest,  and  a  moderate 
diet.'  Whereunto  I  answer,  that  a  moderate  dyet  is  alwaies 
good,  but  not  a  precise  dyet:  for  a  moderate  diet  is,  as  Terence 
speaketh  in  Andria:  To  take  nothing  too  much:  which  al- 
waies is  to  be  observed.  But  if  a  man  accustome  himselfe  to 
such  meats  and  drinks  as  at  length  will  breed  some  incon- 
venience in  his  bodie,  or  to  sleepe  or  to  watch,  or  any  other 
thing  concerning  the  order  of  his  life,  such  custome  must 
naedes  be  amended  and  changed,  yet  with  good  discretion, 
and  not  upon  the  sudden:  because  sudden  changes  bring 
harme  and  weaknesse,  as  Hippocrates  teacheth.  He  there- 
fore that  will  alter  any  custome  in  dyet  rightly,  must  do  it 
with  three  conditions,  which  are  expressed  by  Hippocrates. 
Change  is  profitable,  if  it  be  rightly  used,  that  is,  if  it  be 
done  in  the  time  of  health,  and  at  leisure,  and  not  upon  the 
sudden." 

This  noteworthy  book  written  by  Cogan  was  preceded  by 
the  writings  of  Louis  Cornaro,  the  Venetian,  who  forty  years 
before  had  published  the  first  edition  of  his  celebrated  book, 
"The  Temperate  Life,"  and  who  was  a  most  ardent  advocate 
of  the  benefits  to  be  derived  by  living  temperately,  especially 
in  matters  of  diet.  The  simple  diet  ^hich  served  for  the 


DIETARY  HABITS  169 

nourishment  of  the  oldest  peoples  of  Syria,  Greece,  Egypt, 
and  of  the  Romans  when  they  were  at  the  height  of  their 
prosperity  and  culture,  was  advocated  by  Cornaro  as  conduc- 
ing to  longevity,  better  health,  and  greater  comfort  of  mind 
and  body.  Himself  a  striking  example  of  the  effects  of  a 
reasonable  abstinence  in  diet  (the  last  edition  of  his  book 
having  been  written  at  the  age  of  ninety-five),  his  teachings 
have  continued  to  attract  attention  down  to  the  present  day ; 
and  although  we  have  no  values  in  grams  or  calories  expres- 
sive of  his  average  food  consumption,  it  is  quite  evident  that 
Cornaro  lived  a  very  abstemious  life,  eating  little  of  the  heavier 
articles  of  diet  common  to  his  time  and  country.  It  is  perhaps 
not  strictly  physiological  to  refer  to  these  cases,  yet  they  have 
value  as  representing  a  sentiment,  common  to  the  centuries 
now  passed,  that  benefit  was  to  be  derived  by  mankind  from 
greater  care  in  the  taking  of  food;  that  prevalent  customs 
and  habits  were  leading  the  people  into  intemperate  modes  of 
life,  and  that  these  were  surely  tending  toward  the  physical 
and  mental  deterioration  of  the  nation.  We  may  attach  much 
or  little  weight  to  these  conclusions,  but  there  is  a  certain 
degree  of  significance  in  the  views,  current  then  as  now,  that 
dietetic  customs  and  habits  have  no  real  connection  with 
bodily  requirements. 

Passing  down  to  our  own  times,  we  find  physiologists,  by 
the  aid  of  scientific  methods,  studying  the  effects  of  smaller 
amounts  of  food  (smaller  than  custom  prescribes)  on  the 
condition  of  the  body,  thereby  evincing  a  certain  degree  of 
skepticism  concerning  the  dietary  standards  based  on  habit 
and  usage.  This  has  been  especially  true  regarding  the 
nitrogen  requirement,  or  the  need  for  proteid  food.  As  has 
been  clearly  pointed  out  in  other  connections,  there  are  two 
distinct  needs  which  the  body  has  for  food ;  one  for  proteid 
or  nitrogen,  the  other  for  energy-yielding  material.  Accord- 
ing to  the  Voit  standard,  a  man  of  average  body-weight  doing 


170  THE  NUTRITION  OF  MAN 

a  moderate  amount  of  work  requires  daily  118  grams  of  pro- 
teid  food,  or  about  16  grams  of  metabolizable  nitrogen,  with 
fat  and  carbohydrate  sufficient  to  yield  a  total  fuel  value  of  over 
3000  large  calories.  As  we  have  seen,  the  fuel  value  of  the 
food  must  of  necessity  be  a  variable  quantity  because  of  varia- 
tions in  bodily  activity.  The  more  muscular  work  performed, 
the  greater  must  be  the  intake  of  carbohydrate  and  fat,  if  the 
body  is  to  be  kept  in  equilibrium.  With  proteid  or  nitrogen, 
however,  the  case  is  quite  different,  since  with  adequate 
amounts  of  non-nitrogenous  food,  proteid  is  not  drawn  upon 
for  the  energy  of  muscular  work.  We  can  conceive  of  the 
nitrogen  requirement,  therefore,  as  being  a  constant  factor 
in  the  well-nourished  individual  and  dependent  primarily 
upon  body- weight,  or  more  exactly,  upon  the  weight  of  true 
proteid -containing  tissue.  Obviously,  whatever  else  happens, 
there  must  be  enough  proteid  food  taken  daily  to  maintain 
the  body  in  nitrogen  equilibrium.  If  this  can  be  accomplished 
only  by  the  ingestion  of  16  grams  of  metabolizable  nitrogen, 
then  it  is  plain  that  the  daily  ration  must  contain  at  least  118 
grams  of  proteid  food;  i.  e.,  it  must  conform  approximately 
at  least  to  ordinary  usage. 

This  question  has  been  studied  by  many  investigators, 
with  very  interesting  and  suggestive  results.  Thus,  in  1887, 
Hirschfeld  1  reported  some  experiments  on  himself,  twenty- 
four  years  of  age  and  weighing  73  kilos.  His  ordinary  diet 
contained  daily  100  to  130  grams  of  proteid,  and  the  amount 
of  nitrogen  excreted  varied  from  16  to  20  grams  per  day, 
corresponding  to  a  metabolism  of  proteid  equal  to  the  amount 
ingested.  In  other  words,  the  body  was  essentially  in  nitro- 
gen equilibrium.  Then,  for  a  period  of  fifteen  days,  during 
which  he  was  unusually  active,  he  lived  on  a  diet  in  which 
the  content  of  proteid  corresponded  to  only  6  grams  of  nitro- 

i  Felix  Hirschfeld :  Untersuchungen  iiber  den  Eiweissbedarf  des  Menschen. 
Pfliiger's  Archiv  f.  d.  gesammte  Physiologic,  Band  41,  p.  633. 


TRUE  FOOD   REQUIREMENTS  171 

gen  per  day,  and  yet  he  remained  in  nitrogen  equilibrium. 
The  diet  made  use  of  was  composed  essentially  of  milk,  eggs, 
rice,  potatoes,  bread,  butter,  sugar,  and  coffee,  with  some  wine 
and  beer,  and  on  two  days  a  little  meat.  It  is  to  be  observed 
that  the  nitrogen  or  proteid  intake  per  day  was  only  one-third 
of  what  he  was  accustomed  to  consume.  In  a  second  experi- 
ment, covering  ten  days,  similar  results  were  obtained.  So 
that  evidence  was  afforded  that  a  young  and  vigorous  man 
can  maintain  his  body  in  nitrogen  equilibrium,  for  fifteen  con- 
secutive days  at  least,  on  an  amount  of  proteid  food  equal  to 
only  one-third  of  the  minimal  requirement  called  for  by  com- 
mon usage.  Plainly,  the  difference  between  a  daily  consump- 
tion of  118  grams  of  proteid  food  and  40  grams  represents  a 
large  percentage  saving,  both  of  proteid  and  in  the  metabolism 
of  proteid  matter  with  all  the  attendant  transformations.  In 
these  experiments,  however,  the  subject  consumed  relatively 
large  amounts  of  non-nitrogenous  food,  notably  butter,  of 
which  on  some  days  he  took  as  much  as  100  grams.  The 
average  fuel  value  of  his  food  ranged  from  3750  to  3916  cal- 
ories per  day;  a  fact  of  some  importance,  since  it  is  to  be 
remembered  that  both  fat  and  carbohydrate  tend  to  protect 
proteid  metabolism. 

In  an  experiment  reported  in  1889  by  Carl  Voit1,  on  a 
vegetarian  weighing  about  57  kilos,  it  was  found  that  with 
a  purely  vegetable  diet  the  subject  was  able,  for  a  few  days 
at  least,  to  maintain  his  body  in  essentially  a  condition  of 
nitrogen  equilibrium  on  a  daily  diet  containing  8.4  grams 
of  nitrogen,  corresponding  to  52.5  grams  of  proteid.  In  ad- 
dition, there  was  a  large  consumption  of  starchy  food  with 
some  fat.  Klemperer,2  experimenting  with  two  young  men, 


1  Carl  Voit :  Ueber  die  Kost  eines  Vegetariers.    Zeitschrift  fur  Biologie, 
Band  25,  p.  232. 

2  Klemperer :  Untersuehungen  iiber  Stoff  wechsel  und  Ernahrung  in  Krank- 
heiten.    Zeitschrift  fur  klin.  Medizin,  Band  16,  p.  550. 


172  THE  NUTRITION  OF  MAN 

having  a  body-weight  of  64  and  65.5  kilos,  respectively,  was 
able  to  keep  them  in  a  condition  of  nitrogenous  equilibrium 
for  a  period  of  eight  days  on  4.38  grams  and  3.58  grams  of 
nitrogen  per  day.  The  diet,  however,  had  a  large  fuel  value, 
5020  calories  per  day,  and  contained  in  addition  to  the  small 
amount  of  proteid,  264  grams  of  fat,  470  grams  of  carbohy- 
drate, and  172  grams  of  alcohol.  Breisacher,1  in  an  experi- 
ment on  himself,  using  a  mixed  diet  composed  of  67.8  grams 
of  proteid,  494.2  grams  of  carbohydrate,  and  60.5  grams  of  fat 
per  day,  with  a  total  fuel  value  of  2866  calories,  observed 
a  daily  excretion  of  nitrogen  during  thirty  days  of  8.23  grams. 
This  corresponds  to  a  metabolism  of  51.4  grams  of  proteid, 
thus  showing  that  the  67  grams  of  food-proteid  taken  was 
quite  sufficient  to  maintain  nitrogen  equilibrium  for  the 
above  length  of  time. 

Caspari  and  Glassner2  have  reported  observations  made  on 
two  vegetarians,  a  man  and  his  wife,  aged  49  and  48  years 
respectively,  who  had  lived  for  some  years  exclusively  on  a 
vegetable  diet.  The  man  had  a  body-weight  of  68.8  kilos, 
while  the  woman  weighed  58  kilos.  During  five  days,  the 
man  consumed  per  day,  on  an  average,  7.83  grams  of  nitrogen 
and  4559  calories.  This  corresponds  to  0.114  gram  of  nitro- 
gen per  kilo  of  body-weight,  and  66  calories  per  kilo.  On 
this  diet,  the  man  gained  slightly  in  weight  and  showed  a  plus 
nitrogen  balance  of  5.2  grams  for  the  five  days.  In  other 
words,  even  this  low  nitrogen  or  proteid  intake  was  more  than 
sufficient  to  meet  the  wants  of  his  body.  The  wife,  during 
the  same  period  of  time,  consumed  per  day  5.33  grams  of 
nitrogen  and  2715  calories,  corresponding  to  0.092  gram  of 
nitrogen  per  kilo  of  body-weight  and  47  calories  per  kilo. 


1  L.  Breisacher:    Ueber  die  Grosse  des  Eiweissbedarfs  beim  Menschen. 
Deutsche  med.  Wochenschrift.     1891.    No.  48. 

2  W.  Caspari :  Physiologische  Studien  iiber  Vegetarianismus.    Bonn.   1906. 
p.  13. 


TEUE  FOOD  KEQUIEEMENTS  173 

On  this  diet,  the  woman  gained  0. 9  kilo  in  weight  during  the 
five  days,  and  like  the  man,  she  showed  a  plus  nitrogen 
balance  of  2.45  grams  for  the  entire  period.  The  somewhat 
noted  experiments  of  Sive*n  have  been  referred  to  in  another 
connection,  and  it  will  suffice  to  recall  the  fact  that  he  was 
able,  with  a  body-weight  of  60  kilos,  to  establish  nitrogen 
equilibrium  on  6.26  grams  of  nitrogen,  and  for  a  day  or  two 
on  4.5  grams  of  nitrogen,  with  a  total  fuel  value  of  only 
2444  calories  in  the  day's  ration. 

These  few  illustrations  will  serve  to  indicate  that,  so  far 
as  the  maintenance  of  nitrogen  equilibrium  is  concerned  dur- 
ing short  periods  of  time,  there  is  no  necessity  for  the  con- 
sumption of  proteid  food  in  such  amounts  as  common  usage 
dictates.  The  high  proteid  intake  called  for  by  the  "  stan- 
dard dietaries, "  and  the  ordinary  practices  of  mankind,  is  not 
needed  to  establish  a  condition  of  nitrogen  equilibrium.  It 
would  seem,  however,  as  if  results  of  this  nature,  presented 
from  time  to  time  by  various  investigators,  have  been  con- 
sidered more  in  the  light  of  scientific  curiosities  than  as  data 
having  an  important  bearing  on  physiological  processes.  So 
strong  has  been  the  hold  upon  the  medical  and  physiological 
mind  of  the  necessity  of  high  proteid  that  such  figures  as  the 
above  have  merely  excited  comment,  without  weakening  in 
any  measure  the  prevalent  conviction  that  health,  strength, 
and  the  power  to  work  necessitate  a  high  rate  of  proteid 
exchange. 

To  one  willing  to  accept  the  data  as  having  possible  sig- 
nificance there  arises  at  once  the  question,  How  long  can 
the  body  be  maintained  in  nitrogen  equilibrium  on  such  rela- 
tively small  quantities  of  proteid  food  ?  In  other  words,  can 
experiments  of  this  nature,  extending  over  comparatively 
short  periods  of  time,  be  safely  accepted  as  a  reliable  means 
of  measuring  the  proteid  requirements  of  the  body  for  indefi- 
nite periods?  Suppose,  says  the  critic,  we  grant  that  the 


174  THE   NUTRITION   OF  MAN 

body  can  maintain  itself  in  nitrogen  equilibrium  for  a  week 
or  two  on  a  very  small  amount  of  proteid  food,  what  proof 
have  we  that  in  the  long  run  the  body  will  be  benefited  thereby, 
or  even  able  to  exist  in  a  condition  of  normal  strength  and 
vigor?  In  other  words,  is  a  low  proteid  diet,  one  that  seems 
sufficient  to  maintain  the  body  in  nitrogen  equilibrium,  a 
wholly  safe  one  to  follow  ?  May  there  not  be  other  elements 
to  be  considered,  aside  from  nitrogen  equilibrium,  which,  if 
fully  understood,  would  satisfactorily  account  for  the  customs 
of  mankind,  in  which  perhaps  man's  instincts  have  been  fol- 
lowed for  the  betterment  of  the  race  ?  It  was  with  a  view 
to  learning  more  concerning  these  questions  that  five  years 
ago  the  writer  commenced  systematic,  experimental,  work 
upon  the  nutrition  of  man,  with  special  reference  to  his  nitro- 
gen requirements.  The  experiments  and  observations  have 
been  continued  up  to  the  present  time,  with  many  suggestive 
results,  some  of  which  will  now  be  referred  to.1 

One  group  of  subjects  was  composed  of  professional  men, 
professors  and  instructors  in  the  university,  whose  work  was 
mainly  mental  rather  than  physical,  though  by  no  means 
excluding  the  latter.  Of  this  group,  two  cases  will  be  re- 
ferred to  with  some  regard  for  detail,  since  in  no  other  way 
can  so  striking  a  picture  be  presented  of  the  effects  produced. 
The  first  subject  weighed  65  kilos  in  the  fall  of  1902,  and  at 
that  time  was  nearly  47  years  of  age.  His  dietetic  habits 
were  in  accord  with  common  practice,  and  his  daily  consump- 
tion of  proteid  food  averaged  close  to  118  grams.  With  a 
clear  recognition  of  the  principle  that  the  habits  of  a  life- 
time should  not  be  too  suddenly  changed,  a  very  gradual  re- 
duction in  the  total  amount  of  food,  and  especially  of  proteid 
matter,  was  made.  This  finally  resulted,  with  this  particular 

1  In  presenting  the  general  results  of  these  experiments,  the  writer  has 
drawn  freely  from  his  book,  "  Physiological  Economy  in  Nutrition,"  published 
by  the  Frederick  A.  Stokes  Company,  New  York,  1904. 


TRUE  FOOD   REQUIREMENTS  175 

subject,  in  the  complete  abolition  of  breakfast,  with  the  ex- 
ception of  a  small  cup  of  coffee.  A  light  lunch  was  taken 
at  noontime,  followed  by  a  more  substantial  dinner  at  night. 
There  was  no  change  to  a  vegetable  diet,  but  naturally  any 
attempt  to  cut  off  largely  the  amount  of  proteid  food  neces- 
sarily results  in  a  marked  diminution  in  the  quantity  of 
animal  food  or  meats.  It  is  a  somewhat  singular  though 
suggestive  fact,  that  a  change  of  this  order  gradually  results 
in  a  stronger  liking  for  simple  foods,  with  their  more  delicate 
flavor,  accompanied  by  a  diminished  desire  for  the  heavier 
animal  foods. 

As  the  day's  ration  was  gradually  reduced  in  amount, 
the  body-weight  began  to  fall  off,  until  after  some  months 
it  became  stationary  at  57  kilos,  at  which  point  it  has 
remained  practically  constant  for  over  three  years.  The 
sixteen  pounds  of  weight  lost  was  composed,  mainly  at 
least,  of  superfluous  fat.  For  a  period  of  nine  months,  from 
October,  1903,  to  the  end  of  June,  1904,  the  amount  of  pro- 
teid material  broken  down  in  the  body  was  determined  each 
day.  The  average  daily  metabolism  of  nitrogen  for  the  en- 
tire period  of  nearly  nine  months  amounted  to  5.69  grams. 
For  the  last  two  months,  it  averaged  5.4  grams  per  day. 
Analyses  made  from  time  to  time  since  these  figures  were 
obtained  show  that  the  subject  is  still  living  at  the  same  low 
level  of  nitrogen  metabolism.  In  fact,  the  data  available 
afford  satisfactory  proof  that  for  a  period  covering  over  three 
years  this  particular  person  has  subsisted  on  an  amount  of 
proteid  food  equal  to  a  metabolism  of  not  more  than  5.8 
grams  of  nitrogen  per  day.  It  may  be  asked  why  the  subject 
should  have  continued  such  a  low  proteid  diet  after  the  ni;.e 
months'  period  was  completed?  In  reply,  it  may  be  said 
that  the  new  habit  has  taken  a  firm  hold,  and  entirely  sup- 
planted the  dietetic  desires  and  cravings  of  the  preceding 
years.  Further,  the  improved  condition  of  health,  freedom 


176 


THE   NUTRITION   OF  MAN 


from  minor  ailments  that  formerly  caused  inconvenience  and 
discomfort,  and  the  greater  ability  to  work  without  fatigue, 
have  all  combined  to  place  the  new  habit  on  a  firm  basis, 
from  which  there  is  no  desire  to  change. 

Consider  for  a  moment  what  this  lowered  consumption  of 
proteid  food  really  amounts  to,  as  compared  with  ordinary 
usage  and  the  so-called  dietary  standards.  The  latter  call 
for  at  least  118  grams  of  proteid  or  albuminous  food  daily, 
of  which  105  grams  should  be  absorbable,  in  order  to  main- 
tain the  body  in  a  condition  of  nitrogen  equilibrium,  and  in 
a  state  of  physical  vigor  and  general  tone.  This  would 
mean  a  daily  metabolism  and  excretion  of  at  least  16  grams 
of  nitrogen.  Our  subject,  however,  excreted  per  day,  during 
nine  months,  only  5.69  grams  of  nitrogen,  which  means  a 
metabolism  of  35.6  grams  of  proteid;  i.  e.,  about  one-third 
the  amount  ordinarily  deemed  necessary  to  meet  man's  re- 
quirement for  proteid  food.  But  was  our  subject  in  nitro- 
gen equilibrium  on  this  small  amount  of  proteid  food  ?  We 
answer  yes,  as  the  following  balance  period  shows: 

Output. 

(rVeight  of  Excre- 
ment (dry). 

3.6  grams. 

12.0 
18.5 
23.0 
16.9 
74.0  grams  contain 

6.42%  N. 
4.75  grams  nitrogen. 


Nitrogen  in 
Food. 

Nitrogen  throuf 
Kidneys. 

March  20 

6.989  grams. 

5.91  grams. 

21 

6.621 

5.52 

22 

6.082 

5.94 

23 

6.793 

5.61 

24 

5.057 

4.31 

25 

6.966 

5.39 

38.508 


32.68 


38.508  grams  nitrogen.      37.43  grams  nitrogen. 

Nitrogen  balance  for  six  days        =        +1-078  grams. 
Nitrogen  balance  per  day  =        -f  0.179  gram. 


TKUE  FOOD  KEQUIBEMENTS 


177 


In  this  particular  period  of  six  days,  the  body  was  really 
gaining  a  little  nitrogen,  i.  e.,  storing  away  a  small  amount 
of  proteid  for  future  use,  although  it  may  be  granted  that 
the  amount  was  too  small  to  have  any  special  significance. 
During  this  period,  the  average  daily  intake  of  nitrogen  was 
6.4  grams,  equal  to  40  grams  of  proteid  food.  The  average 
daily  output  of  nitrogen  through  kidneys  and  excrement  was 
6.24  grains.  The  average  daily  output  of  metabolized  nitro- 
gen, through  the  kidneys,-  was  5.44  grams,  corresponding  to 
the  breaking  down  of  84  grams  of  proteid  material.  Further, 
it  should  be  stated  that  the  total  calorific  value  of  the  daily 
food  during  this  period  was  less  than  2000  calories.  Let 
me  add  now  a  final  balance  period  taken  at  the  close  of  the 
nine  months'  trial: 


Nitrogen  in 
Food. 

June  23 

6.622  grams. 

24 

6.331 

25 

4.941 

26 

5.922 

27 

5.486 

Output. 

Nitrogen  through    Weight  of  Excre- 
Kidneys. 

5.26  grams. 
5.30 
4.43 
4.66 


29.302 


4.98 


24.63 


ment  (dry). 

10.6  grams. 

30.7 

14.2 

11.9 

15.2 

82.6  grams  contain 

6.08%  N. 
5.022  grams  nitrogen. 


29.302  grams  nitrogen.     29.652  grams  nitrogen. 

Nitrogen  balance  for  five  days        =        —0.350  gram. 
Nitrogen  balance  per  day  =        —0.070  gram. 


In  this  period  of  five  days,  the  average  daily  intake  of 
nitrogen  was  5.86  grams,  corresponding  to  36.6  grams  of 
proteid  food.  The  average  daily  output  of  metabolized  nitro- 
gen was  4.92  grams,  implying  the  breaking  down  in  the  body 

12 


178  THE  NUTRITION   OF  MAN 

of  only  30.7  grams  of  proteid  material  per  day.  The  fuel 
value  of  the  daily  food,  calculated  as  closely  as  possible,  was 
less  than  2000  calories.  The  body  was  essentially  in  nitro- 
gen equilibrium,  the  minus  balance  being  too  small  to  have 
any  special  significance. 

It  will  be  instructive  to  consider  next  the  actual  character 
and  amount  of  the  diet  made  use  of  on  several  of  these 
balance  days: 

March  21. 

Breakfast.  —  Coffee  119  grams,  cream  30  grams,  sugar  9  grama. 

Lunch. —One  shredded  wheat  biscuit  31  grams,  cream  116  grams,  wheat  gem 

33  grams,  butter  7  grams,  tea  185  grams,  sugar  10  grams,  cream  cake 

53  grams. 
Dinner. — Pea  soup  114  grams,  lamb  chop  24  grams,  boiled  sweet  potato  47 

grams,  wheat  gems  76  grams,  butter  13  grams,  cream  cake  52  grams, 

coffee  61  grams,  sugar  10  grams,  cheese  crackers  16  grams. 

Total  nitrogen  content  of  the  day's  food  =  6.621  grams. 

June  S4. 

Breakfast.  —  Coffee  96  grams,  cream  32  grams,  sugar  8  grams. 

Lunch.  —  Creamed  codfish  89  grams,  baked  potato  95  grams,  butter  10  grams, 

hominy  gems  58  grams,  strawberries  86  grams,  sugar  26  grams,  ginger 

snaps  47  grams,  water. 
Dinner.  —  Cold  tongue  14  grams,  fried  potato  48  grams,  peas  60  grams,  wheat 

gems  30  grams,  butter  11  grams,  lettuce-orange  salad  with  mayonnaise 

dressing  155  grams,  crackers  22  grams,  cream  cheese  14  grams,  ginger 

snaps  22  grams,  coffee  58  grams,  sugar  10  grams. 

Total  nitrogen  content  of  the  day's  food  =  6.331  grams. 
June  %5. 

Breakfast.  —  Coffee  101  grams,  cream  36  grams,  sugar  13  grams. 

Lunch.  —  Omelette  50  grams,  bacon  9  grams,  French  fried  potato  23  grams, 

biscuit  29  grams,  butter  8  grams,  ginger  snaps  42  grams,  cream  cheese 

17  grams,  iced  tea  150  grams,  sugar  15  grams. 
Dinner.  —  Wheat  popovers   57  grams,  butter  10  grams,  lettuce-orange  salad 

with  mayonnaise  dressing  147  grams,  crackers  22  grams,  cream  cheese 

21  grams,  cottage  pudding  82  grams,  coffee  48  grams,  sugar  11  grams. 

Total  nitrogen  content  of  the  day's  food  =  4.941  grams. 


TKUE  FOOD  KEQUIKEMENTS  179 

June  27. 

Breakfast.  —  Coffee  112  grams,  cream  22  grams,  sugar  10  grams. 

Lunch.  —  Roast  lamb  9  grams,  baked  potato  90  grams,  wheat  gems  47  grams, 
butter  12  grams,  iced  tea  250  grams,  sugar  25  grams,  vanilla  eclair  47 
grams. 

Dinner.  —  Lamb  chop  32  grams,  creamed  potato  107  grams,  asparagus  49 
grams,  bread  35  grams,  butter  17  grams,  lettuce-orange  salad  with  may- 
onnaise dressing  150  grams,  crackers  21  grams,  cream  cheese  12  grams, 
coffee  63  grams,  sugar  9  grams. 

Total  nitrogen  content  of  the  day's  food  =  5.486  grams. 

It  can  be  seen  that  there  was  nothing  especially  peculiar 
in  these  dietaries,  aside  from  their  simplicity,  except  that  the 
quantities  were  small.  Meat  was  not  excluded;  there  was 
no  approach  to  a  cereal  diet;  there  were  no  fads  involved, 
nothing  but  simple  moderation  in  the  amounts  of  nitrogen- 
containing  foods.  Further,  there  was  perfect  freedom  of 
choice ;  full  latitude  to  consider  personal  likes  and  dislikes  in 
the  selection  of  foods ;  anything  that  appealed  to  the  appetite 
could  be  eaten,  with  the  simple  restriction  that  the  amount 
taken  must  be  small.  During  the  balance  days,  naturally, 
every  article  of  food  had  to  be  carefully  weighed  and  ana- 
lyzed, which  fact  undoubtedly  tended  to  limit  in  some  degree 
the  variety  of  foods  chosen,  since  increase  in  the  number  of 
articles  meant  increased  labor  in  analysis.  Quite  noticeable, 
however,  was  the  extreme  constancy  in  the  nitrogen-content 
of  the  daily  diet,  even  on  those  days  when  the  food  was  not 
weighed.  In  other  words,  there  had  been  gradually  acquired 
a  new  habit  of  food  consumption,  and  the  individual,  uncon- 
sciously perhaps,  rarely  overstepped  the  limits  fixed  by  the 
new  level  of  proteid  metabolism.  This  is  a  fact  that  has  been 
conspicuous  in  nearly  all  of  our  experiments,  where  freedom 
of  choice  in  the  taking  of  food  has  been  followed ;  and  is  in 
harmony  with  the  view  that  after  a  lower  level  of  proteid 
metabolism  has  once  been  established,  and  the  body  has 
become  accustomed  to  the  new  conditions,  there  is  little  ten- 


180  THE  NUTRITION   OF  MAN 

dency  for  any  marked  deviation  from  the  new  standards  of 
food  consumption. 

With  maintenance  of  body-weight,  together  with  nitrogen 
equilibrium  through  all  these  months;  and  with  health, 
strength,  and  mental  and  physical  vigor  unimpaired,  there  is 
certainly  ground  for  the  belief  that  the  real  needs  of  the  body 
were  as  fully  met  by  the  lowered  consumption  of  proteid  food 
as  by  the  quantities  called  for  by  the  customary  standards. 
Finally,  it  should  be  noted  that  this  particular  subject  was 
small  in  weight,  and  hence  did  not  need  so  much  proteid  as 
a  man  of  heavier  body- weight  would  require.  In  recognizing 
this  principle,  we  may  for  future  comparison  calculate  the 
nitrogen  requirement  of  the  body,  on  the  basis  of  the  present 
results,  per  kilo  of  body-weight.  With  the  weight  of  the 
subject  placed  at  57  kilos,  and  with  an  average  daily  excre- 
tion of  nitrogen  amounting  to  practically  5.7  grams,  it  is 
plain  that  this  individual  was  quite  able  to  maintain  a 
condition  of  equilibrium  with  a  metabolism  of  0.1  gram  of 
nitrogen  per  kilo  of  body-weight.  Translated  into  terms  of 
proteid  matter,  this  would  mean  a  utilization  by  the  body 
of  0.625  gram  of  proteid  daily  per  kilo  of  body- weight.  Re- 
garding the  fuel  value  of  the  daily  food,  we  need  not  be 
more  precise  than  to  emphasize  the  fact  that  so  far  as  could 
be  determined,  on  the  basis  of  chemical  composition,  the 
heat  value  of  the  food  rarely  exceeded  1900  calories  per 
day.  If  we  make  a  liberal  allowance,  for  the  sake  of  pre- 
caution, it  would  seem  quite  safe  to  say  that  this  particular 
individual,  under  the  conditions  of  life  and  bodily  activity 
prevailing,  did  not  apparently  need  of  fuel  value  more  than 
2000  calories  per  day,  which  would  correspond  to  35  calories 
per  kilo  of  body-weight. 

Let  us  turn  now  to  the  second  subject  in  this  group,  a 
man  of  76  kilos  body-weight,  32  years  of  age,  and  of  strong 
physique.  His  active  life  in  the  laboratory  called  for  greater 


TKUE  FOOD  KEQUIREMENTS  181 

physical  exertion  than  the  former  subject,  and  consequently 
there  was  need  for  greater  consumption  of  non-nitrogenous 
food,  with  the  accompanying  increase  in  fuel  value  of  the 
day's  ration.  As  in  the  preceding  case,  there  was  no  pre- 
scribing of  food,  but  a  gradual  and  voluntary  diminution  of 
proteid  material.  During  the  last  seven  months  and  a  half 
of  the  experiment,  the  average  daily  excretion  of  nitrogen 
through  the  kidneys  amounted  to  6.53  grams,  equivalent  to 
a  metabolism  of  40.8  grams  of  proteid  matter  daily;  a  little 
more  than  one-third  the  minimal  quantity  called  for  by  com- 
mon usage.  At  first,  the  body-weight  of  the  subject  gradu- 
ally fell  until  it  reached  70  kilos,  at  which  point  it  remained 
fairly  constant  during  the  last  five  months.  That  the  quan- 
tity of  food  taken  was  quite  sufficient  to  maintain  the  body 
in  a  condition  of  nitrogen  equilibrium  is  apparent  from  the 
results  of  a  comparison  of  income  and  outgo  of  nitrogen,  as 
shown  in  the  following  table: 

Output. 

Nitrogen  in    Nitrogen  through    Weight  of  Excre- 
ment (dry). 

14  grams. 

39 

30 

83  contain  6.06%  N.  =  5.03  grm.  N. 


57 

95  contain  5.76%  N.  =  5.47  grm.  N. 

1050  grm.  N. 

57.343  44.18    +    10.50  grams  nitrogen. 

67.343  grams  N.  64.68  grams  nitrogen. 

Nitrogen  balance  for  seven  days        =        +2.663  grams. 
Nitrogen  balance  per  day  =        +0.380  gram. 


Food. 

Kidneys. 

May  18 

8.668  grams. 

6.06  grams. 

19 

6.474 

7.17 

20 

6.691 

6.33 

21 

8.345 

6.78 

22 

7.015 

6.70 

23 

9.726 

5.75 

24 

10.424 

6.39 

182  THE  NUTRITION  OF  MAN 

The  average  daily  intake  of  nitrogen  was  8.192  grams, 
equivalent  to  51.2  grams  of  proteid  food.  The  average 
amount  of  nitrogen  excreted  through  the  kidneys  each  day 
was  6.31  grams,  corresponding  to  a  metabolism  of  39.43 
grams  of  proteid  matter.  The  plus  balance  of  0.380  gram  of 
nitrogen  per  day  shows  that  not  only  was  the  amount  of  proteid 
food  consumed  quite  adequate  to  meet  the  demands  of  the 
body,  but  the  latter  was  able  to  store  up  2.3  grams  of  proteid 
per  day.  Regarding  the  character  of  the  food  taken  by  this 
subject,  it  should  be  stated  that  there  was  gradually  developed 
a  tendency  toward  a  pure  vegetarian  diet.  During  the  last 
seven  months  of  the  experiment,  meats  were  almost  entirely 
excluded.  The  diet  voluntarily  selected  thus  differed  de- 
cidedly from  that  of  the  preceding  subject  in  that  it  was 
much  more  bulky,  contained  a  larger  proportion  of  undiges- 
tible  vegetable  matter,  and  was  richer  in  fats  and  carbohy- 
drates, with  a  corresponding  increase  in  fuel  value.  The 
exact  character  of  the  daily  dietary  is  indicated  by  the  fol- 
lowing data  of  food  consumption,  on  four  of  the  days  of  the 
above  balance  period: 

May  19. 

Breakfast.  —  Banana  102  grams,  wheat  rolls  50  grams,  coffee  150  grams,  cream 

50  grams,  sugar  21  grams. 
Lunch.  —  Omelette  20  grams,  bread  57  grams,  hominy  137  grams,  syrup  68 

grams,  potatoes  128  grams,  coffee  100  grams,  cream  50  grams,  sugar 

21  grams. 
Dinner.  —  Tomato  puree  200  grams,  bread  24  grams,  fried  sweet  potato  100 

grams,  spinach  70  grams,  Indian  meal  100  grams,  syrup  25  grams,  coffee 

100  grams,  cream  40  grams,  sugar  21  grams. 

Total  nitrogen  content  of  the  day's  food  =  6.474  grams. 

May  W. 

Breakfast.  —  Sliced  orange  140  grams,  coffee  100  grams,  cream  30  grams,  sugar 

21  grams. 
Lunch.  —  Lima  beans  40  grams,  mashed  potato  250  grams,  bread  28  grams, 

fried  hominy  115  grams,  syrup  48  grams,  coffee  100  grams,  cream  30 

grams,  sugar  21  grams. 


TKUE  FOOD  KEQUIREMENTS  183 

Dinner.  —  Consomme  150  grams,  string  beans  140  grams,  mashed  potato  250 
grams,  rice  croquette  93  grains,  syrup  25  grams,  cranberry  jam  95  grams, 
bread  19  grams,  coffee  100  grams,  cream  30  grams,  sugar  21  grams. 

Total  nitrogen  content  of  the  day's  food  =  6.691  grams. 

May  21. 

Breakfast.  —  Banana  153  grams,  coffee  150  grams,  cream  30  grams,  sugar  21 

grams. 
Lunch.  —  Potato  croquette   229  grams,  bread  25  grams,  tomato  123  grams, 

Indian  meal  109  grams,  syrup  48  grams,  coffee  100  grams,  cream  20 

grams,  sugar  14  grams. 
Dinner.  — Bean  soup  100  grams,  bacon  5  grams,  fried  potato  200  grams,  bread 

31  grams,  lettuce-orange  salad  47  grams,  prunes  137  grams,  coffee  100 

grams,  cream  25  grams,  sugar  21  grams,  banana  255  grams. 

Total  nitrogen  content  of  the  day's  food  =  8.345  grams. 

May  23. 

Breakfast.  —  Banana  229  grams,  coffee  125  grams,  cream  25  grams,  sugar  21 
grams. 

Lunch.  —  Consomme  75  grams,  scrambled  egg  15  grams,  bread  58  grams,  apple 
sauce  125  grams,  fried  potato  170  grams,  rice  croquette  197  grams,  syrup 
68  grams,  coffee  100  grams,  cream  30  grams,  sugar  21  grains. 

Dinner.  —  Vegetable  soup  100  grams,  potato  croquette  198  grams,  bread  73 
grams,  bacon  7  grams,  string  beans  120  grams,  water  ice  77  grams, 
banana  270  grams,  coffee  100  grams,  cream  30  grams,  sugar  14  grams. 

Total  nitrogen  content  of  the  day's  food  =  9.726  grams. 

While  the  critic  might  justly  say  that  these  dietaries  lack 
variety  and  would  not  appeal  to  a  fastidious  taste,  there  is 
force  in  the  •  illustration  which  they  afford  of  a  simple  diet 
being  quite  adequate  to  meet  the  wants  of  the  body.  Fur- 
ther, it  should  be  emphasized  that  there  is  no  special  virtue 
in  any  of  these  dietaries,  aside  from  their  simplicity  and  low 
content  of  nitrogen.  They  represent  individual  taste  and 
selection.  Any  other  form  of  diet  would  answer  as  well, 
provided  there  was  not  too  large  an  intake  of  proteid,  and 
provided  further  the  fuel  value  of  the  day's  ration  was  suffi- 
cient to  meet  the  requirements  for  heat  and  work.  Again, 
it  might  be  said  that  with  this  latter  subject  the  daily  con- 


184  THE  NUTRITION  OF  MAN 

sumption  of  proteid  food  was  considerably  larger  than  with 
the  first  subject.  This  is  indeed  true,  but  it  must  be  re- 
membered that  the  second  subject  had  a  body-weight  of  70 
kilos  during  the  last  seven  months,  while  the  first  subject 
weighed  only  57  kilos.  Obviously,  with  this  marked  differ- 
ence in  the  weight  of  living  tissue  there  must  be  a  corre- 
sponding difference  in  the  extent  of  proteid  katabolism,  and 
consequently  a  difference  in  the  demand  for  proteid  food. 

As  we  have  seen,  the  smaller  subject  for  a  period  of  many 
months  showed  a  proteid  katabolism  equal  to  0.1  gram  of 
nitrogen,  per  kilo  of  body-weight,  daily.  The  second  and 
larger  subject,  on  a  totally  different  diet,  for  seven  months 
and  a  half,  metabolized  daily,  on  an  average,  6.53  grams  of 
nitrogen.  Taking  the  weight  of  the  body  at  70  kilos,  it  is 
readilv  seen  that  the  nitrogen  metabolized  daily  per  kilo  of 
body- weight  was  0.093  gram,  almost  identical  with  the  rate 
of  nitrogen  exchange  found  with  the  first  subject.  It  is  cer- 
tainly very  suggestive  that  these  two  individuals  with  their 
marked  difference  in  body-weight,  under  different  degrees  of 
physical  activity,  and  living  on  different  forms  of  diet,  with 
only  the  one  point  in  common  of  voluntary  restriction  in  the 
amount  of  proteid  food,  until  a  new  habit  had  been  acquired 
and  a  new  level  of  proteid  metabolism  attained,  should  have 
quite  independently  reached  exactly  the  same  level  of  nitro- 
gen exchange  per  kilo  of  body- weight.  And  when  it  is  re- 
membered that  this  was  attained  by  the  daily  consumption 
of  not  more  than  one-third  to  one-half  the  minimal  amount 
of  proteid  food  called  for  by  the  dietetic  customs  of  man- 
kind, and  with  maintenance  of  all  the  characteristics  of  good 
health  through  this  comparatively  long  period  of  time,  there 
certainly  seems  to  be  justification  for  the  opinion  that  the 
consumption  of  proteid  food,  as  practised  by  the  people  of  the 
present  generation,  is  far  in  excess  of  the  needs  of  the  body. 
Referring  for  a  moment  to  the  calorific  value  of  the  food 


TRUE  FOOD  REQUIREMENTS  185 

used  by  the  second  subject,  in  the  last  balance  period,  it  is 
to  be  noted  that  the  heat  value  per  day  averaged  2448  calo- 
ries, as  estimated  on  the  basis  of  the  chemical  composition 
of  the  food.  This  would  amount  to  34  calories  per  kilo. 
Whether  this  figure  is  strictly  correct  is  immaterial;  it  is 
certainly  sufficiently  so  to  warrant  the  statement  that  the 
needs  of  the  body  were  fully  met  by  an  intake  of  food  below 
the  standards  set  by  usage,  and  that  maintenance  of  nitrogen 
equilibrium  on  a  greatly  diminished  consumption  of  proteid 
food  is  possible  without  increasing  the  intake  of  non-nitroge- 
nous matter. 

Finally,  as  affording  additional  evidence,  we  may  refer  to 
a  third  subject  in  this  group,  a  man  of  65  kilos  body-weight, 
26  years  of  age,  who  for  a  period  of  six  consecutive  months 
maintained  body-weight,  nitrogen  equilibrium,  and  a  general 
condition  of  good  health,  with  a  proteid  metabolism  equal  to 
7.81  grams  of  nitrogen  per  day.  During  the  last  two  months 
of  the  experiment,  the  average  excretion  of  nitrogen  per  day 
amounted  to  6.68  grams,  corresponding  to  a  metabolism  of 
0.102  gram  of  nitrogen  per  kilo  of  body-weight.  This  figure, 
it  will  be  noted,  is  practically  identical  with  the  values  ob- 
tained with  the  preceding  subjects,  calculated  to  the  same 
unit  of  weight.  Further,  this  third  subject  did  not  reduce 
his  nitrogen  intake  by  an  exclusion  of  meat,  but  made  use  of 
his  ordinary  diet  gradually  reduced  in  amount.  His  daily 
consumption  of  proteid  food  averaged  55  grams,  or  8.83  grams 
of  nitrogen,  and  on  this  amount  of  proteid,  without  increasing 
the  intake  of  fats  and  carbohydrates,  he  was  quite  able  to  do 
his  work  with  preservation  of  physiological  equilibrium. 

Views  so  radically  different  from  those  commonly  accepted 
can  be  made  to  carry  weight,  only  by  the  accumulation  of  sup- 
porting evidence  obtained  under  widely  different  conditions 
of  life,  and  by  methods  which  will  defy  criticism.  It  might 
be  argued,  and  with  perhaps  some  justification,  that  while 


186  THE  NUTRITION  OF  MAN 

professional  men,  with  freedom  from  muscular  work,  may  be 
able  to  live  without  detriment  on  a  relatively  small  amount 
of  proteid  food,  such  a  conclusion  would  not  be  warranted 
for  the  great  majority  of  mankind  with  their  necessarily 
greater  muscular  activity.  We  are  confronted  at  once  with 
the  oft-heard  statement  that  the  laboring  man  requires  more 
proteid  food ;  he  has  a  more  vigorous  appetite,  and  he  must 
take  an  abundance  of  meat  and  other  foods  rich  in  proteid,  if 
he  is  to  maintain  his  ability  as  a  worker.  Note  the  state- 
ments already  made  in  other  connections  regarding  the  food 
consumption  of  Maine  lumbermen,  of  men  on  the  football 
team,  of  trained  athletes  in  general.  These  men  consume 
large  amounts  of  proteid  daily,  because  their  work  de- 
mands it.  If  the  demand  did  not  really  exist,  they  would 
not  so  agree  in  the  use  of  high  proteid  standards,  so  runs 
the  argument.  The  custom  certainly  does  exist  and  is 
almost  universally  followed;  men  in  training  for  athletic 
events  deem  it  necessary  to  consume  large  amounts  of  pro- 
teid food.  Custom  and  long  experience  sanction  a  high 
proteid  diet,  rich  in  nitrogen,  for  the  development  and  main- 
tenance of  that  strength  and  vigor  that  help  to  make  the 
accomplished  athlete.  It  is  common  knowledge  to-day,  how- 
ever, that  the  energy  of  muscle  work  does  not  have  its  origin 
in  the  breaking  down  of  proteid  material,  certainly  not  when 
there  is  an  adequate  amount  of  fat  and  carbohydrate  in  the 
diet.  A  high  proteid  intake  must  therefore  be  called  for 
because  of  some  subtle  quality,  not  at  present  fully  under- 
stood. It  must  not  be  subjected  to  criticism,  however,  be- 
cause it  is  sanctioned  by  custom,  habit,  and  common  usage. 

Still,  I  have  ventured  to  experiment  somewhat  with  a 
group  of  eight  university  athletes,  all  trained  men,  and  with 
some  surprising  results.  We  have  not  space  for  details,  but 
it  may  be  mentioned  that  the  men  were  young,  from  22  to  27 
years  of  age,  and  were  experts  in  some  field  of  athletic  work. 


TEUE  FOOD  KEQUIKEMENTS  187 

By  a  preliminary  study  of  their  ordinary  dietetic  habits,  it 
was  found  that  they  were  all  large  consumers  of  proteid  food, 
with  a  corresponding  high  rate  of  proteid  katabolism.  One 
subject  of  92  kilos  body-weight,  during  ten  days,  showed  an 
average  daily  excretion  through  the  kidneys  of  22.79  grams 
of  nitrogen,  implying  a  metabolism  of  142  grams  of  proteid 
matter  per  day.  On  one  of  these  days,  the  nitrogen  excretion 
reached  the  high  figure  of  31.99  grams,  corresponding  to  a 
metabolism  of  about  200  grams  of  proteid  matter.  Calcu- 
lated per  kilo  of  body-weight,  this  means  a  metabolism  of 
0.35  gram  of  nitrogen,  or  three  and  a  half  times  the  amount 
needed  by  the  three  professional  men  for  the  maintenance 
of  nitrogen  equilibrium.  These  subjects,  with  an  intelligent 
comprehension  of  the  point  at  issue,  and  with  full  freedom 
in  the  choice  of  food,  gradually  diminished  their  daily  con- 
sumption of  proteid  material,  at  the  same  time  cutting  down 
very  markedly  the  total  consumption  of  food.  The  experi- 
ment extended  through  five  months,  and  during  the  last  two 
months,  the  average  daily  excretion  of  metabolized  nitrogen  of 
the  eight  men  amounted  to  8.81  grams  per  man.  This  corre- 
sponds to  a  metabolism  of  55  grams  of  proteid  matter. 

Further,  the  average  daily  output  of  nitrogen  through  the 
kidneys  during  the  preceding  two  months  was  in  many  cases 
nearly,  if  not  quite,  as  low  as  during  the  last  two  months  of 
the  experiment.  If  we  contrast  this  average  daily  exchange 
of  8.81  grams  of  nitrogen  with  the  average  output  prior  to 
the  change  in  diet,  it  is  easy  to  see  that  the  men  were  liv- 
ing on  about  one-half  the  amount  of  proteid  food  they  were 
formerly  accustomed  to  take.  Moreover,  if  the  metabolized 
nitrogen  for  each  individual,  with  one  exception,  is  calcu- 
lated per  kilo  of  body-weight,  it  is  seen  to  vary  from  0.108 
gram  to  0.134  gram;  somewhat  higher  than  was  observed  with 
the  older  professional  men,  but  not  conspicuously  so.  Again, 
it  is  to  be  emphasized  that  the  lowered  intake  of  proteid  food 


188  THE  NUTRITION  OF  MAN 

with  these  men  was  quite  adequate  to  maintain  their  bodies 
in  nitrogen  equilibrium.  We  may  cite  a  single  case  by  way 
of  illustration: 


Output. 


May  18 

Nitrogen  of 
Food. 
8.119  grams. 

Nitrogen  throug 
Kidneys. 
6.75  grama. 

19 

9.482 

6.64 

20 

10.560 

8.46 

21 

8.992 

8.64 

22 

9.025 

8.53 

23 

8.393 

7.69 

24 

7.284 

7.34 

ment  (dry). 
..  grams. 
15 


_24 

128  grams  contain 

6.40  %  N. 

61.855  63.04        +        8.192  grams  nitrogen. 

61.855  grams  nitrogen.    61.232  grams  nitrogen. 

Nitrogen  balance  for  seven  days        =        +0.623  gram. 
Nitrogen  balance  per  day  =        +0.089  gram. 

The  daily  intake  of  nitrogen  during  this  balance  period 
averaged  8.83  grams,  corresponding  to  55.1  grams  of  proteid 
food.  The  metabolized  nitrogen  eliminated  through  the  kid- 
neys averaged  7.58  grams  per  day,  thus  showing  a  daily  aver- 
age metabolism  of  47.37  grams  of  proteid  matter.  With  a 
body-weight  of  63  kilos,  this  individual  was  maintaining 
equilibrium  on  a  metabolism  of  0.120  gram  of  nitrogen  per 
kilo  of  body-weight.  The  fuel  value  of  the  day's  food  as 
estimated  did  not  exceed  2800  calories,  thus  substantiating 
the  general  statement  that  there  is  no  need  for  increasing  the 
fuel  value  of  the  food  in  any  attempt  to  maintain  a  lower 
nitrogen  level.  This  particular  individual,  in  his  choice  of 
food,  unconsciously  drifted  —  as  he  expressed  it  —  toward  a 
simple  vegetable  diet,  without,  however,  excluding  meat  en- 


TKUE  FOOD  KEQUIKEMENTS  189 

tirely.     The  following  four  dietaries  will  serve  to  illustrate 
the  character  and  amount  of  his  daily  food: 

May  21. 

Breakfast.  —  Banana  106  grams,  boiled  Indian  meal   150  grams,  cream  60 

grams,  sugar  21  grams,  bread  59  grams,  butter  16  grams. 
Lunch.  —  Lamb  chop  37  grams,  potato  croquette  105  grams,  tomato  216  grams, 

bread  55  grams,  butter  13  grams,  sugar  14  grams,  water  ice  143  grams. 
Dinner.  —  Bean  soup  100  grams,  bacon  10  grams,  fried  egg  22  grams,  fried 

potato   100  grams,  lettuce  salad  63  grams,  coffee  100  grams,  cream   50 

grams,  sugar  21  grams,  stewed  prunes  247  grams. 

Total  nitrogen  content  of  the  day's  food  =  8.992  grams. 

May  %%. 

Breakfast.  —  Orange  60  grams,  oatmeal  207   grams,  roll  46  grams,  butter  14 

grams,  coffee  150  grams,  cream  150  grams,  sugar  35  grams. 
Lunch.  —  Boiled   potato   150  grams,  boiled  onions   145   grams,  macaroni  130 

grams,  fried  rice  138  grams,  syrup  48  grams,  ice  cream  160  grams,  cake 

26  grams. 
Dinner.  —  Celery  soup   150  grams,  spinach   100  grams,   mashed  potato   100 

grams,  bread  19  grams,  coffee  100  grams,  cream  50  grams,  sugar  7  grams, 

strawberry  short-cake  169  grams. 

Total  nitrogen  content  of  the  day's  food  =  9.025  grams. 

May  23. 

Breakfast.  —  Sliced  banana   201   grams,  cream  100  grams,  sugar  28  grams, 

griddle  cakes  103  grams,  syrup  48  grams. 
Lunch.  —  Consomme  150  grams,  rice  croquette  140  grams,  syrup  48  grams,  fried 

potato  100  grams,  bread  36  grams,  butter  15  grams,  apple  sauce  90  grams, 

coffee  75  grams,  sugar  7  grams. 
Dinner.  —  Vegetable   soup   100  grams,  bacon  20  grams,  potato  croquette  50 

grams,  string  beans   120  grams,  macaroni   104  grams,  bread  26  grams, 

water  ice  184  grams. 

Total  nitrogen  content  of  the  day's  food  =  8.393  grams. 

May  %4. 

Breakfast.  —  Orange  80  grams,  fried  rice  186  grams,  syrup  72  grams,  coffee  100 

grams,  cream  50  grams,  sugar  21  grams. 
Lunch.  —  Celery  soup  125  grams,  bread  34  grams,  butter  19  grams,  boiled  onion 

127   grams,  boiled  potato   150  grams,  tomato  sauce  50  grams,  stewed 

prunes  189  grams,  cream  50  grams. 


190  THE  NUTRITION   OF  MAN 

Dinner. — Tomato  soup  125  grams,  bread  21  grams,  fried  potato  100  grams, 
spinach  130  grams,  cream  pie  168  grams,  coffee  100  grams,  cream  60 
grams,  sugar  14  grams. 

Evening.  —  Ginger  ale  250  grams. 

Total  nitrogen  content  of  the  day's  food  =  7.284  grams. 

Here,  again,  we  have  dietaries  not  particularly  attractive  to 
every  one,  but  they  represent  the  choice  of  an  individual  who 
was  following  his  own  preferences,  and  like  the  preceding 
dietaries  they  are  characterized  by  simplicity.  In  any  event, 
they  were  quite  adequate  for  the  wants  of  the  body,  and 
their  value  to  us  lies  in  the  proof  they  afford  that  a  rela- 
tively small  intake  of  proteid  food  will  not  only  bring  about 
and  maintain  nitrogen  equilibrium  for  many  months,  and 
probably  indefinitely,  but  that  such  a  form  of  diet  is  equally 
as  effective  with  vigorous  athletes,  accustomed  to  strenuous 
muscular  effort,  as  with  professional  men  of  more  sedentary 
habits.  Further,  these  many  months  of  observation  with 
different  individuals  all  lead  to  the  opinion  that  there  are 
no  harmful  results  of  any  kind  produced  by  a  reduction  in 
the  amount  of  proteid  food  to  a  level  commensurate  with  the 
actual  needs  of  the  body.  Body- weight,  health,  physical 
strength,  and  muscular  tone  can  all  be  maintained,  in  partial 
illustration  of  which  may  be  offered  two  photographs  of  one 
of  the  eight  athletes  taken  toward  the  end  of  the  experiment ; 
pictures  which  are  certainly  the  antithesis  of  enfeebled  mus- 
cular structure,  or  diminished  physical  vigor. 


STAPLETON 

Photograph  taken  in  the  middle  of  the  experiment,  in  April 


CHAPTER  VI 

FURTHER  EXPERIMENTS  AND  OBSERVATIONS 
BEARING   ON   TRUE   FOOD   REQUIREMENTS 

TOPICS  :  Dietary  experiments  with  a  detail  of  soldiers  from  the  United 
States  army.  General  character  of  the  array  ration.  Samples  of  the 
daily  dietary  adopted.  Rate  of  nitrogen  metabolism  attained.  Effect 
on  body-weight.  Nitrogen  balance  with  lowered  proteid  consumption. 
Influence  of  low  proteid  on  muscular  strength  of  soldiers  and  athletes. 
Effect  on  fatigue.  Effect  on  physical  endurance.  Fisher's  experi 
ments  on  endurance.  Dangers  of  underfeeding.  Dietary  observa- 
tions on  fruitarians.  Observations  on  Japanese.  Recent  dietary 
changes  in  Japanese  army  and  navy.  Observations  of  Dr.  Hunt  on 
resistance  of  low  proteid  animals  to  poisons.  Conclusions. 

GENERAL  acceptance  of  a  new  theory,  or  a  new  point 
of  view,  can  be  expected  only  when  there  is  an  ade- 
quate amount  of  scientific  evidence  on  which  the  theory  can 
safely  rest.  Facts  cannot  be  ignored,  and  the  larger  the 
amount  of  supporting  evidence  the  more  certain  becomes  the 
general  truth  of  the  theory  to  which  it  points.  Corrobora- 
tive evidence,  therefore,  is  always  desirable,  and  he  who 
would  open  up  a  new  point  of  view  must  be  zealous  in  ac- 
cumulating facts  to  uphold  his  position.  Critics  there  are 
without  number  who  are  ever  ready  to  pick  flaws  in  an  argu- 
ment or  overturn  a  theory,  especially  if  the  one  or  the  other 
stands  opposed  to  their  own  point  of  view.  This,  however, 
is  highly  advantageous  for  the  advance  of  sound  knowledge, 
since  it  necessarily  prompts  the  advocate  to  search  in  all 
directions  for  added  data,  by  which  he  can  build  a  bulwark 


192  THE  NUTRITION  OF  MAN 

of  fact  sufficient  to  defy  just  criticism.  Further,  the  true 
scientific  spirit  demands  persistent  and  painstaking  effort  in 
the  search  after  truth,  that  error  and  misconception  may  be 
avoided. 

In  harmony  with  these  ideas,  our  attempt  to  ascertain 
the  real  needs  of  the  body  for  proteid  food  led  us  to  enlarge 
our  evidence  by  a  series  of  experiments  with  still  another 
body  of  men,  i.  e.,  a  detail  of  soldiers  from  the  United  States 
army.1  This  was  a  somewhat  more  difficult  and  ambitious 
undertaking,  since  the  number  of  subjects  involved  was 
larger,  and  because  with  this  group  of  men  we  could  not 
expect  quite  that  high  degree  of  intelligent  co-operation 
afforded  by  the  preceding  subjects.  Still,  this  very  fact  was 
in  a  sense  an  added  inducement,  since  it  offered  the  oppor- 
tunity of  experimenting  with  a  body  of  men  who  naturally 
would  not  take  kindly  to  anything  that  looked  like  depriva- 
tion, and  whose  continued  co-operation  could  be  expected 
only  by  satisfying  their  natural  demands  for  food.  If  this 
could  be  accomplished  by  an  intelligent  prescription  in  their 
daily  diet,  and  the  experiment  brought  to  a  successful  con- 
clusion, with  maintenance  of  body -weight,  nitrogen  equi- 
librium, health,  strength,  and  general  vigor;  with  an  intake 
of  proteid  food  essentially  equal  to  that  adopted  by  the  pre- 
ceding subjects,  corroborative  evidence  of  the  highest  value 
would  be  obtained. 

The  detail  was  composed  of  a  detachment  of  twenty  men 
from  the  Hospital  Corps  of  the  army,  under  the  command 
of  a  first  lieutenant  and  assistant  surgeon.  They  were  located 
in  a  convenient  house  near  to  the  laboratory,  where  they  lived 
during  their  six  months'  stay  in  New  Haven,  under  military 
discipline,  and  subject  to  the  constant  surveillance  of  the 


1  In  presenting  the  general  results  of  these  experiments,  the  writer  has 
drawn  freely  from  his  book,  "  Physiological  Economy  in  Nutrition,"  published 
by  the  Frederick  A.  Stokes  Company,  New  York,  1904. 


TRUE  FOOD  KEQUIREMENTS  193 

commanding  officer  and  the  non-commissioned  officers.  Hav- 
ing well-trained  cooks  and  assistants,  with  all  necessary 
facilities  for  preparing  and  serving  their  food,  with  members 
of  the  laboratory  staff  to  superintend  the  weighing  of  the 
food  as  it  was  placed  before  the  men,  and  with  intelligent 
clerks  to  attend  to  the  many  details  connected  with  such  an 
undertaking,  a  somewhat  unique  physiological  experiment 
was  started.  Thirteen  members  of  the  detachment  really 
took  part  in  the  experiment  as  subjects,  and  they  represented 
a  great  variety  of  types:  of  different  ages,  nationalities, 
temperaments,  and  degrees  of  intelligence.  They  were  men 
accustomed  to  living  an  active  life  under  varying  conditions, 
and  they  naturally  had  great  liking  for  the  pleasures  of  eat- 
ing. Further,  it  should  be  remembered  that,  although  the 
men  had  volunteered  for  the  experiment,  they  had  no  per- 
sonal interest  whatever  in  the  principles  involved,  and  it 
could  not  be  expected  that  they  would  willingly  incom- 
mode themselves,  or  suffer  any  great  amount  of  personal  in- 
convenience. Again,  there  were  necessary  restrictions  placed 
upon  their  movements,  when  relieved  from  duty,  which  con- 
stituted something  of  a  hardship  in  the  minds  of  many  of  the 
men  and  added  to  the  irksomeness  and  monotony  of  their 
daily  life.  Regularity  of  life  was  insisted  upon,  and  this 
was  a  condition  which  brought  to  some  of  the  men  a  new 
experience.  These  facts  are  mentioned  because  their  recital 
will  help  to  make  clear  that,  from  the  standpoint  of  the  men, 
there  were  certain  depressing  influences  connected  with  the 
experiment  which  would  add  to  any  personal  discomfort 
caused  by  restriction  of  diet. 

The  ordinary  army  ration  to  which  these  men  were  accus- 
tomed was  rich  in  proteid,  especially  in  meat,  and  during  the 
first  few  days  they  were  allowed  to  follow  their  usual  dietary 
habits,  in  order  that  data  might  be  obtained  bearing  on  their 
average  food  consumption.  The  details  of  one  day's  food 

13 


194  THE  NUTRITION  OF  MAN 

intake  will  suffice  to  show  the  average  character  and  amount 
of  the  food  eaten  per  man : 

Breakfast.  —  Beefsteak  222  grams,  gravy  68  grams,  fried  potatoes  234  grams, 
onions  34  grams,  bread  144  grams,  coffee  679  grams,  sugar  18  grams. 

Dinner.  —  Beef  171  grams,  boiled  potatoes  350  grams,  onions  55  grams,  bread 
234  grams,  coffee  916  grams,  sugar  27  grams. 

Supper.  —  Corned  beef  195  grams,  potatoes  170  grams,  onions  21  grams,  bread 
158  grams,  fruit  jelly  107  grams,  coffee  450  grams,  sugar  21  grams. 

It  is  not  necessary  to  comment  upon  the  large  proportion 
of  proteid  matter  in  the  day's  ration;  the  three  large  por- 
tions of  meat  testify  clearly  enough  to  that  fact,  while  the 
three  equally  large  volumes  of  coffee  indicate  a  natural  dis- 
position toward  generous  consumption  of  anything  available. 
Habit,  reinforced  by  inclination,  had  evidently  placed  these 
men  on  a  high  plane  of  food  consumption. 

For  a  period  of  six  months,  a  daily  dietary  was  prescribed 
for  the  subjects;  the  food  for  each  meal  and  for  every  man 
being  of  known  composition,  each  article  being  carefully 
weighed,  while  the  content  of  nitrogen  in  the  day's  ration 
was  so  graded  as  to  bring  about  a  gradual  reduction  in  the 
amount  of  proteid  ingested.  The  rate  of  proteid  katabolism 
was  likewise  determined  each  day  by  careful  estimation  of 
the  excreted  nitrogen,  balance  experiments  being  made  from 
time  to  time  in  order  to  ascertain  if  the  men  were  in  a  con- 
dition of  nitrogen  equilibrium.  Finally,  it  should  be  men- 
tioned that  the  subjects  lived  a  fairly  active  life,  having 
each  day  a  certain  amount  of  prescribed  exercise  in  the 
university  gymnasium,  in  addition  to  the  regular  drill  and 
other  duties  associated  with  their  usual  work. 

As  just  stated,  the  amount  of  proteid  food  was  gradually 
reduced,  three  weeks  being  taken  to  bring  the  amount  down 
to  a  level  somewhat  commensurate  with  the  estimated  needs 
of  the  body.  This  naturally  resulted  in  diminishing  largely 
the  intake  of  meat,  thonfifh  by  no  moans  o-ntirolv  excluding1 


TRUE  FOOD   REQUIREMENTS  195 

it.  Effort  was  constantly  made  to  introduce  as  much  variety 
as  was  possible  with  simple  foods,  though  the  main  problem 
with  this  group  of  men  was  to  keep  the  volume  of  the  food 
up  to  such  a  point  as  would  dispel  any  notion  that  they 
were  not  having  enough  to  eat.  A  second  problem,  which 
at  first  threatened  trouble,  was  the  fear  of  the  men,  as  they 
saw  the  proportion  of  meat  gradually  drop  off,  that  they  were 
destined  to  lose  their  strength;  but  fortunately,  they  very 
soon  began  to  realize  that  their  fears  in  this  direction  were 
groundless,  and  a  little  later  their  personal  experience  opened 
their  eyes  to  possible  advantages  which  quickly  drove  away 
all  further  thought  of  danger,  and  made  them  quite  content 
to  continue  the  experiment.  We  may  introduce  here  a  few 
samples  of  the  daily  food  given  to  the  men  after  they  had 
reached  their  lower  level  of  proteid  intake: 

January  15. 

Breakfast.  —  Wheat  griddle  cakes  200  grams,  syrup  50  grams,  one  cup  coffee 1 

350  grams. 
Dinner.  —  Codfish  balls  (4  parts  potato,  1  part  fish,  fried  in  pork  fat)  150  grams, 

stewed  tomato  200  grams,  bread  75  grams,  one  cup  coffee  350  grams, 

apple  pie  95  grams. 
Supper.  —  Apple  fritters  200  grams,  stewed  prunes  125  grams,  bread  50  gram?, 

butter  15  grams,  one  cup  tea  350  grams. 

Total  nitrogen  content  of  the  day's  food  =  8.560  grams. 

January  16. 

Breakfast.  —  Soft  oatmeal  150  grams,  milk  100  grams,  sugar  30  grams,  bread 

30  grams,  butter  10  grams,  one  cup  coffee  350  grams. 
Dinner.  —  Baked  macaroni  with  a  little  cheese  200  grams,  stewed  tomato  200 

grams,  bread  50  grams,  tapioca-peach  pudding  150  grams,  one  cup  coffee 

350  grams. 
Supper.  —  Fried  bacon  20  grams,  French  fried  potato  100  grams,  bread  75 

grams,  jam  75  grams,  one  cup  tea  350  grams. 

Total  nitrogen  content  of  the  day's  food  =  7.282  grams. 
1  The  coffee  was  prepared  with  milk  and  sugar.    • 


196  THE   NUTRITION  OF  MAN 

March  1. 

Breakfast.  —  Fried  rice  160  grams,  syrup  50  grams,  baked  potato  150  grams, 

butter  10  grams,  one  cup  coffee  360  grams. 
Dinner.  —  Thick  pea  soup  250  grams,  boiled  onions  150  grams,  boiled  sweet 

potato  150  grams,  bread  75  grams,  butter  20  grams,  one  cup  coffee  350 

grams. 
Supper.  —  Celery-lettuce-apple  salad  120  grams,  crackers  32  grams,  American 

cheese  20  grams,  potato  chips  79  grams,  one  cup  tea  350  grams,  rice 

custard  100  grams. 

Total  nitrogen  content  of  the  day's  food  =  7.825  grams. 

March  3. 

Breakfast.  — Boiled  hominy  175  grams,  milk  125  grams,  sugar  25  grams,  baked 

potato  150  grams,  butter  10  grams,  one  cup  coffee  350  grams. 
Dinner.  —  Hamburg  steak  with  much  bread,  fat,  and  onions  150  grams,  boiled 

potato  250  grams,  bread  75  grams,  butter  10  grams,  one  cup  coffee  350 

grams. 
Supper.  —  Tapioca-peach  pudding  250  grams,  bread  75  grams,  butter  20  grams, 

jam  75  grams,  one  cup  tea  350  grams. 

Total  nitrogen  content  of  the  day's  food  =:  8.750  grama. 

March  6. 

Breakfast.  —  Sliced  banana  100  grams,  fried  Indian  meal  150  grams,  syrup  50 

grams,  baked  potato  150  grams,  butter  10  grams,  one  cup  coffee  350 

grams. 
Dinner.  —  Corned  beef  50  grams,  boiled  cabbage  200  grams,  mashed  potato  250 

grams,  bread  75  grams,  fried  rice  100  grams,  jam   75  grams,  one  cup 

coffee  350  grams. 
Supper.  —  Crackers  32  grams,  butter  10  grams,  sardine  14  grams,  sponge  cake 

150  grams,  apple  sauce  150  grams,  one  cup  tea  350  grams. 
Total  nitrogen  content  of  the  day's  food  =  10.265  grams. 

March  SO. 

Breakfast.  —  Sliced  banana  260  grams,  fried  hominy  150  grams,  butter  10 
grams,  syrup  75  grams,  one  cup  coffee  350  grams. 

Dinner.  —  Codfish  balls  125  grams,  mashed  potato  250  grams,  stewed  tomato 
200  grams,  bread  35  grams,  apple  sauce  200  grams,  one  cup  coffee  350 
grams. 

Supper.  —  Chopped  fresh  cabbage  with  salt,  pepper,  and  vinegar  75  grams, 
bread  60  grams,  butter  20  grams,  fried  sweet  potato  250  grams,  cran- 
berry sauce  200  grams,  sponge  cake  50  grams,  one  cup  tea  350  grama 
Total  nitrogen  content  of  the  day's  food  =  9.356  grams. 


TRUE  FOOD  REQUIREMENTS  197 

March  31. 

Breakfast.  —  Fried  Indian  meal  100  grams,  syrup  75  grams,  baked  potato  250 

grams,  butter  20  grams,  one  cup  coffee  350  grams. 
Dinner.  —  Tomato  soup,  thick,  with  potatoes  and  onions  boiled  in,  300  grams, 

scrambled  egg  50  grams,  mashed  potato  200  grams,  bread  50  grams, 

butter  10  grams,  one  cup  coffee  350  grams. 
Supper.  —  Fried  bacon  20  grams,  boiled  potato  200  grams,  butter  10  grams, 

bread  pudding  150  grams,  sliced  banana  200  grams,  one  cup  tea  860 

grams. 
Total  nitrogen  content  of  the  day's  food  =  8.420  grams. 

April  1. 

Breakfast.  —  Fried  hominy  150  grams,  syrup  75  grams,  baked  potato  200  grams, 

butter  20  grams,  one  cup  coffee  350  grams. 
Dinner.  —  Baked  spaghetti  200  grams,  mashed  potato  250  grams,  boiled  turnip 

150  grams,  bread  35  grams,  butter  10  grams,  apple  sauce  200  grams,  one 

cup  coffee  350  grams. 
Supper.  —  Fried  bacon  25  grams,  fried  sweet  potato  200  grams,  bread  35  grams, 

butter  20  grams,  jam  100  grams,  apple-tapioca  pudding  300  grams,  one 

cup  tea  350  grams. 
Total  nitrogen  content  of  the  day's  food  =  7.342  grams. 

These  dietaries  are  fair  sr  joples  of  the  daily  food  given  the 
men  during  the  last  fivp  months  of  the  experiment.  If  we 
place  the  intake  of  nitrogen  at  8.5  grams  per  day,  or  even  9 
grams  daily,  it  would  mean  at  the  most  an  average  daily  con- 
sumption of  56  grams  of  proteid;  viz.,  about  one-third  the 
amount  they  were  accustomed  to  take  under  their  ordinary 
modes  of  life.  Of  greater  interest,  however,  is  the  rate  of 
proteid  katabolism  shown  by  these  men  under  the  above 
conditions  of  diet,  during  the  five  months'  period.  The 
average  daily  output  of  metabolized  nitrogen  for  each  man 
ranged  from  7.03  grams  —  the  lowest  —  to  8.91  grams  —  the 
highest.  An  excretion  of  7.03  grams  of  nitrogen  per  day 
means  a  katabolism,  or  breaking  down,  of  43.9  grams  of  pro- 
teid matter;  while  the  excretion  of  8.91  grams  of  nitrogen 
corresponds  to  a  katabolism  of  55.6  grams  of  proteid.  The 
grand  average,  i.  e.,  the  average  daily  output  of  nitrogen 


198  THE  NUTRITION  OF  MAN 

of  all  the  men  for  the  five  months'  period  amounted  to  7.8 
grams  per  man,  corresponding  to  an  average  daily  katabolism 
of  48. 75  grams  of  proteid.  The  heaviest  man  of  the  group 
had  a  body-weight  of  74  kilograms,  while  his  average  daily 
output  of  metabolized  nitrogen  amounted  to  7.84  grams. 
This  corresponds  to  0.106  gram  of  metabolized  nitrogen  per 
kilo  of  body -weight;  a  figure  which  agrees  quite  closely  with 
the  lowest  figures  obtained  with  the  preceding  subjects  when 
calculated  to  the  same  unit  of  weight.  Many  of  the  men, 
however,  metabolized  considerably  more  nitrogen  or  proteid 
in  proportion  to  their  body-weight,  due  in  a  measure  at  least 
to  the  fact  that  they  were  being  fed  more  liberally  with  pro- 
teid food  than  was  really  necessary  for  the  needs  of  the  body. 
In  this  group,  we  have  a  body  of  men  doing  a  reasonable 
amount  of  physical  work,  who  lived  without  discomfort  for 
five  consecutive  months  on  a  daily  consumption  of  proteid 
food  not  much,  if  any,  greater  than  one-third  the  amount 
called  for  by  common  usage,  and  the  average  fuel  value  of 
which  certainly  did  not  exceed  3000  calories  per  day.  In- 
deed, so  far  as  could  be  determined  on  the  basis  of  chemical 
composition,  the  heat  value  of  the  food  was  quite  a  little 
less  than  this  figure  would  imply. 

If  the  relatively  small  amount  of  proteid  food  made  use  of 
in  this  trial  was  inadequate  for  the  real  necessities  of  the 
body,  some  indication  of  it  would  be  expected  to  reveal  itself, 
with  at  least  some  of  the  men,  by  the  end  of  the  period.  One 
criticism  frequently  made  is  that  the  subject  draws  in  some 
measure  upon  his  store  of  body  material.  Should  this  be  the 
case,  it  is  evident  that  body- weight  —  in  such  a  long  experi- 
ment as  this  —  will  gradually  but  surely  diminish.  Further, 
the  subject  will  show  a  minus  nitrogen  balance,  i.e.,  there  will 
be  a  constant  tendency  for  the  body  to  give  off  more  nitrogen 
than  it  takes  in.  As  bearing  on  the  first  point,  the  following 
table  showing  the  body-weights  of  the  men  at  the  commence- 


TRUE  FOOD  REQUIREMENTS 


199 


ment  of  the  experiment  in  October,  and  at  the  close  of  the 
experiment  in  April  will  be  of  interest : 


TABLE  OF  BODY-WEIGHTS 


October,  1903 

April,  1904 

gteltz           .         

kilos 
52.3 

kilos 

530 

54.0 

55.0 

Coffnifin            •     •     •     • 

591 

580 

59.2 

59.0 

59.4 

61.0 

6Q.1 

590 

61.3 

60.6 

Cohn   

65.0 

62.6 

667 

62.1 

71.3 

71.0 

Fritz        

760 

726 

Bates  

72.7 

643  (Feb.) 

Davis                ... 

593 

57  2  (Jan  ) 

As  is  readily  seen,  five  of  the  men  practically  retained  their 
weight  or  made  a  slight  gain.  Of  the  others,  Coffman,  Loe- 
wenthal,  Sliney,  and  Cohn  lost  somewhat,  but  the  amount  was 
very  small.  Further,  the  loss  occurred  during  the  first  few 
weeks  of  the  experiment,  after  which  their  weight  remained 
practically  stationary.  Fritz  and  Oakman  lost  weight  some- 
what more  noticeably,  but  this  loss  likewise  occurred  during 
the  earlier  part  of  the  trial.  The  accompanying  photographs 
of  Fritz,  taken  at  the  close  of  the  experiment,  show  plainly  that 
such  loss  of  weight  as  he  suffered  did  not  detract  from  the 
appearance  of  his  well-developed  musculature.  Certainly,  the 


200 


THE   NUTRITION   OF   MAN 


photographs  do  not  show  any  signs  of  nitrogen  starvation,  or 
suggest  the  lack  of  any  kind  of  food. 

Of  all  the  men,  Bates  was  the  only  one  who  underwent 
any  great  loss  of  weight.  He,  however,  was  quite  stout,  and 
the  work  in  the  gymnasium,  reinforced  by  the  change  in  diet, 
brought  about  what  was  for  him  a  very  desirable  loss  of  body- 
weight.  It  is  evident,  therefore,  that  there  was  no  marked 
or  prolonged  loss  of  body-weight  as  a  result  of  the  con- 
tinued use  of  the  low  proteid  diet.  Regarding  the  second 
point,  viz.,  nitrogen  equilibrium,  the  following  illustrations 
will  suffice  to  indicate  the  relationship  existing  between  the 
income  and  outgo  of  nitrogen.  A  balance  experiment  with 
each  of  the  men,  lasting  seven  days,  February  29  to  March  6, 
is  here  shown,  the  figures  given  being  the  daily  averages  for 
the  period : 


• 

Nitrogen 
of  Food. 

Nitrogen 
of  Urine. 

Nitrogen  of 
Excrement. 

Nitrogen 
Balance. 

Oakman     .... 

grams 
9.52 

grams 

7.24 

grams 

1.76 

grams 
+0.52 

Henderson     .    .    . 
Morris  

9.40 
9.49 

7.90 
605 

1.00 
230 

+0.50 
4-1  14 

Coffman    .... 
Steltz    

9.53 
9.62 

7.92 
716 

1.47 
1.95 

+0.14 
+051 

Loewenthal    .    .    . 
Cohn     

9.64 
927 

7.00 
763 

1.71 
141 

+0.95 
+023 

Zooman     .... 
Sliney        .... 

9.49 
952 

7.13 
808 

1.76 
192 

+0.60 
048 

Broyles      .... 
Fritz      

9.43 

937 

7.01 
636 

1.19 
181 

+1.23 
+1  20 

With  one  exception,  all  of  the  men  were  plainly  having 
more  proteid  food  than  was  necessary  to  maintain  the  body 


FRITZ 
At  the  close  of  the  experiment 


TRUE  FOOD  REQUIREMENTS 


201 


in  nitrogen  equilibrium,  the  plus  nitrogen  balance  in  most 
cases  being  fairly  large.  It  is  only  necessary  to  remember 
that  a  gain  to  the  body  of  1  gram  of  nitrogen  means  a  laying 
by  of  6.25  grams  of  proteid,  and  with  such  a  gain  per  day  it 
is  apparent  that  the  men  were  really  being  supplied  with  an 
excess  of  proteid  food.  This  view  is  supported  by  the  fact 
that  a  later  balance  experiment,  when  considerably  less  proteid 
food  was  being  given,  still  showed  many  of  the  men  in  a 
condition  of  plus  balance,  or  with  a  minus  balance  so  small  as 
to  indicate  essentially  nitrogen  equilibrium.  The  following 
figures,  being  daily  averages  of  a  balance  period  about  the 
first  of  April,  may  be  offered  in  evidence : 


Nitrogen 
of  Food. 

Nitrogen 
of  Urine. 

Nitrogen  of 
Excrement. 

Nitrogen 
Balance. 

Broyles  

grams 
8.66 

grams 
6.63 

grams 
1.87 

grams 
+016 

Fritz 

813 

577 

163 

+073 

Loewenthal    .    .    . 
Steltz    

8.51 
8.32 

6.51 
6.50 

2.02 
1.88 

-0.02 
—006 

Cohn 

829 

625 

155 

4-049 

8.45 

6.49 

2.27 

—031 

Oakman     .... 

8.62 

7.04 

1.87 

-0.29 

A  daily  intake  of  8.5  grams  of  nitrogen  means  the  con- 
sumption of  53  grams  of  proteid.  Under  these  conditions  of 
diet,  the  average  daily  amount  of  nitrogen  metabolized  was 
6.45  grams,  corresponding  to  40.3  grams  of  proteid.  The  men 
were  practically  in  a  condition  of  nitrogen  equilibrium,  so 
that  we  are  apparently  justified  in  the  general  statement  that 
the  simple  dietary  followed  with  these  men  during  the  six 
months'  experiment,  and  which  was  accompanied  by  an  aver- 
age daily  metabolism,  after  the  first  three  weeks,  of  7.8  grams 
of  nitrogen,  was  certainly  sufficient  to  maintain  both  body- 


202  THE  NUTRITION  OF  MAN 

weight  and  nitrogen  equilibrium.  Lastly,  emphasis  may  be 
laid  upon  the  fact  that  these  values  for  nitrogen  do  not 
necessarily  represent  the  minimal  proteid  requirement  of  the 
human  body,  since  it  is  a  well-established  physiological  prin- 
ciple that  by  increase  of  non-nitrogenous  food  the  rate  of 
proteid  katabolism  can  always  be  further  diminished  ;  a  prin- 
ciple which  is  plainly  in  harmony  with  the  view  that  a  high 
rate  of  proteid  exchange  is  not  a  necessary  requisite  for  the 
welfare  of  the  body. 

The  experimental  results  presented  afford  very  convincing 
proof  that  so  far  as  body- weight  and  nitrogen  equilibrium  are 
concerned,  the  needs  of  the  body  are  fully  met  by  a  consump- 
tion of  proteid  food  far  below  the  fixed  dietary  standards, 
and  still  further  below  the  amounts  called  for  by  the  re- 
corded habits  of  mankind.  General  health  is  equally  well 
maintained,  and  with  suggestions  of  improvement  that  are 
frequently  so  marked  as  to  challenge  attention.  Most  con- 
spicuous, however,  though  something  that  was  entirely  un- 
locked for,  was  the  effect  observed  on  the  muscular  strength 
of  the  various  subjects.  When  the  experiments  were  planned, 
it  was  deemed  important  to  arrange  for  careful  quantitative 
tests  of  the  more  conspicuous  muscles  of  the  body,  with  a 
view  to  measuring  any  loss  of  strength  that  might  occur  from 
the  proposed  reduction  in  proteid  food.  The  thought  that 
prompted  this  action  was  a  result  of  the  latent  feeling  that 
somehow  muscular  strength  must  be  dependent  more  or  less 
upon  the  proteid  constituents  of  the  muscles,  and  that  con- 
sequently the  cutting  down  of  proteid  food  would  inevitably 
be  felt  in  some  degree.  The  most  that  could  be  hoped  for 
was  that  muscle  tone  and  muscular  strength  might  be  main- 
tained unimpaired.  Hence,  we  were  at  first  quite  astonished 
at  what  was  actually  observed. 

With  the  soldier  detail,  fifteen  distinct  strength  tests  were 
made  with  each  man  during  the  six  months'  period,  by 


TRUE  FOOD   REQUIREMENTS 


203 


means  of  appropriate  dynamometer  tests  applied  to  the  mus- 
cles of  the  back,  legs,  chest,  upper  arms,  and  forearms, 
reinforced  by  quarter-mile  run,  vault,  and  ladder  tests,  etc. 
The  so-called  "total  strength"  of  the  man  was  computed 
by  multiplying  the  weight  of  the  body  by  the  number  of 
times  the  subject  was  able  to  push  up  (strength  of  triceps 
muscles)  and  pull  up  (strength  of  biceps  muscles)  his  body 
while  upon  the  parallel  bars,  to  this  product  being  added 
the  strength  (dynamometer  tests)  of  hands,  legs,  back,  and 
chest.  It  should  be  added  that  all  of  these  tests  were 
made  quite  independently  in  the  university  gymnasium  by 
the  medical  assistants  and  others  in  charge  of  the  work  there. 
It  will  suffice  for  our  purpose  to  give  here  the  strength  tests 
of  the  various  members  of  the  soldier  detail  at  the  beginning 
and  close  of  the  experiment-. 


TOTAL   STRENGTH 


October. 

April. 

Broyles      .... 

2560 

5530 

Coffman     .... 

2835 

6269 

Cohn      

2210 

4002 

Fritz      

2504 

6178 

Henderson      .    .    . 

2970 

4598 

Loewenthal    .    .    . 

2463 

5277 

Morris    

2543 

4869 

Oakman     .... 

3445 

5055 

Sliney    

3245 

5307 

Steltz     

2838 

4581 

Zooman      .... 

3070 

5457 

204  THE  NUTRITION  OF  MAN 

Without  exception^  we  note  with  all  of  the  men  a  phenome- 
nal gain  in  strength,  which  demands  explanation.  Was  it 
all  due  to  the  change  in  diet?  Probably  not,  for  these  men 
at  the  beginning  of  the  experiment  were  untrained,  and  it  is 
not  to  be  assumed  that  months  of  practical  work  in  the  gym- 
nasium would  not  result  in  a  certain  amount  of  physical  de- 
velopment, with  corresponding  gain  in  muscular  skill  and 
power.  Putting  this  question  aside  for  the  moment,  however, 
it  is  surely  proper  to  emphasize  this  fact ;  viz.,  that  although 
the  men  for  a  period  of  five  months  were  restricted  to  a  daily 
diet  containing  only  one-third  to  one-half  the  amount  of 
proteid  food  they  had  been  accustomed  to,  there  was  no  loss 
of  physical  strength ;  no  indication  of  any  physical  deteriora- 
tion that  could  be  detected.  In  other  words,  the  men  were 
certainly  not  being  weakened  by  the  lowered  intake  of  proteid 
food.  This  is  in  harmony  with  the  principle,  already  dis- 
cussed, that  the  energy  of  muscle  work  comes  primarily 
from  the  breaking  down  of  non-nitrogenous  material,  and  con- 
sequently a  diminished  intake  of  proteid  food  can  have  no 
inhibitory  effect,  provided,  of  course,  there  is  an  adequate 
amount  of  proteid  ingested  to  satisfy  the  endogenous  require- 
ments of  the  tissues. 

On  the  other  hand,  recalling  the  large  number  of  nitroge- 
nous cleavage  products  which  result  from  the  breaking  down 
of  proteid  material,  we  can  conceive  of  an  exaggerated  ex- 
ogenous proteid  katabolism  which  may  flood  the  tissues  and 
the  surrounding  lymph  with  a  variety  of  nitrogenous  waste 
products,  having  an  inhibitory  effect  upon  the  muscle  fibres 
themselves,  or  upon  the  peripheral  endings  of  the  motor  nerves, 
by  which  the  muscles  are  prevented,  directly  or  indirectly,  from 
working  at  their  highest  degree  of  efficiency.  This  being  true, 
a  reduction  of  the  exogenous  katabolism  to  a  level  more  nearly 
commensurate  with  the  real  needs  of  the  body  might  result  in 
a  marked  increase  in  the  functional  power  of  the  tissue.  How- 


TRUE  FOOD  REQUIREMENTS  205 

ever  this  may  be,  the  fact  remains  that  all  of  the  subjects 
showed  this  great  gain  in  strength ;  and  furthermore,  there 
was  a  noticeable  gain  in  self-reliance  and  courage  in  their 
athletic  work,  both  of  which  are  likewise  indicative  of  an  im- 
proved condition  of  the  body.  How  far  these  improvements 
are  attributable  to  training  and  to  the  more  regular  life  the 
men  were  leading,  and  how  far  to  the  change  in  diet,  cannot 
be  definitely  determined.  We  may  venture  the  opinion,  how- 
ever, for  reasons  to  be  made  clear  shortly,  that  the  change  in 
diet  was  in  a  measure  at  least  responsible  for  the  increased 
efficiency.  As  the  writer  has  already  expressed  it,  there  must 
be  enough  food  to  make  good  the  daily  waste  of  tissue,  enough 
food  to  furnish  the  energy  of  muscular  contraction,  but  any 
surplus  over  and  above  what  is  necessary  to  supply  these  needs 
is  not  only  a  waste,  but  may  prove  an  incubus,  retarding  the 
smooth  working  of  the  machinery  and  detracting  from  the 
power  of  the  organism  to  do  its  best  work. 

Let  us  now  turn  our  attention  for  a  moment  to  the  group 
of  university  athletes,  remembering  that  these  men  had  been 
in  training  for  many  months,  and  some  of  them  for  several 
years,  prior  to  the  commencement  of  the  trial  with  a  reduced 
proteid  intake.  In  the  words  of  the  director  of  the  gymna- 
sium, "  These  eight  men  were  in  constant  practice  and  in  the 
pink  of  condition ;  they  were  in  *  training  form '  when  they 
began  the  changed  diet."  Some  of  them  had  gained  marked 
distinction  for  their  athletic  work;  one  during  the  early 
months  of  the  test  won  the  Collegiate  and  All-around  Inter- 
collegiate Championship  of  America.  Compare  now  the 
strength  tests  of  these  men  as  taken  at  the  beginning  and 
end  of  the  five  months'  experiment,  during  which  they  reduced 
their  daily  intake  of  proteid  food  more  than  fifty  per  cent : 


206 


THE  NUTRITION   OF  MAN 


TOTAL  STRENGTH 


January. 

June. 

G.  W.  Anderson      . 

4913 

5722 

W.  L.  Anderson 

6016 

9472 

Bellis     

6993 

8165 

Callahan    .... 

2154 

3983 

Donahue    .... 

4584 

5917 

Jacobus      .... 

4548 

5667 

Schenker  .... 

5728 

7135 

Stapleton   .... 

5351 

6833 

It  is  to  be  observed  that  the  majority  of  these  trained  men 
showed  at  the  first  trial  in  January  a  total  strength  test  ap- 
proximately equal  to  that  of  the  soldier  detail  at  the  close  of 
their  experiment.  This  by  no  means  implies  that  the  latter 
men  owed  their  gain  in  strength  wholly  to  the  systematic 
training  they  had  undergone,  but  it  is  certainly  plausible  to 
assume  that  in  a  measure  this  was  the  case.  In  any  event,  it 
is  plain  that  the  long-continued  low  proteid  diet  of  the  sol- 
diers had  not  interfered  with  a  progressive  muscular  devel- 
opment, and  the  attainment  of  a  high  degree  of  muscular 
strength. 

The  noticeable  feature  in  the  figures  obtained  with  the  ath- 
letes, however,  is  the  striking  difference  between  the  January 
and  June  results.  Every  man,  without  exception,  showed  a 
decided  gain  in  his  muscular  power  as  measured  by  the  strength 
tests.  This  improvement,  to  be  sure,  was  not  so  marked  as 
with  the  soldiers ;  a  fact  to  be  expected,  since  with  these  men 
the  element  of  training  and  the  acquisition  of  proficiency  in 
athletic  work  could  have  played  no  part  in  the  observed  gain. 
Further,  mDst  of  the  tests  indicated  that  the  gain  was  progres- 


TKUE  FOOD  EEQUIREMENTS  207 

sive,  each  month  showing  an  improvement,  in  harmony  with 
the  growing  effect  of  the  diminished  proteid  intake.  With 
these  subjects,  the  only  tangible  change  in  their  mode  of  life 
which  could  in  any  sense  be  considered  as  responsible  for  their 
gain  in  strength  was  the  change  in  diet.  Consequently,  it 
seems  perfectly  justifiable  to  conclude  that  the  observations 
presented  afford  reasonable  proof  of  the  beneficial  effects  of  a 
lowered  proteid  intake  upon  the  muscular  strength  of  man. 

The  significance  of  such  a  conclusion  is  manifestly  obvious. 
It  confirms  and  gives  added  force  to  the  observations  that 
man  can  profitably  maintain  nitrogen  equilibrium,  and  body- 
weight,  upon  a  much  smaller  amount  of  proteid  food  than  he 
is  accustomed  to  consume.  It  harmonizes  with  the  view  that 
the  normal  requirements  of  the  body  for  food,  under  which 
health,  strength,  and  maximum  efficiency  are  best  maintained, 
are  on  a  far  lower  level  than  the  ordinary  practices  of  man- 
kind would  lead  one  to  believe.  The  widespread  opinion  that 
a  rich  proteid  diet,  with  the  correspondingly  high  rate  of 
proteid  metabolism,  is  a  necessity  for  the  preservation  of 
bodily  strength  and  vigor,  is  seen  to  be  without  foundation  ; 
for  even  the  most  conservative  estimate  of  the  real  value  of 
these  strength  tests  must  carry  with  it  the  conviction  that 
lowering  the  consumption  of  proteid  food  does  not  at  least 
result  in  any  weakening  of  the  body.  This  is  a  fact  of  vital 
importance,  for  it  needs  no  argument  to  convince  even  the 
most  optimistic  that  while  it  might  be  possible  to  maintain 
body- weight  and  nitrogen  equilibrium  on  a  small  amount  of 
proteid  food,  such  a  form  of  physiological  economy  would  not 
only  be  of  no  advantage  to  the  individual,  but  would  be 
positively  injurious  if  there  was  a  gradual  weakening  of  the 
muscles  of  the  body  with  decrease  of  physical  strength,  vigor, 
and  endurance. 

Another  fact  to  be  emphasized  in  this  connection  was  the 
conviction,  gradually  acquired  by  many  of  the  subjects,  that 


208  THE  NUTRITION  OF  MAN 

they  suffered  less  from  fatigue  after  vigorous  muscular  effort 
than  formerly.  This  was  especially  conspicuous  in  the  case 
of  Donahue,  whose  work  on  the  Varsity  basket-ball  team 
called  for  vigorous  exercise.  It  is  interesting  to  note  that 
this  athlete,  of  63  kilos  body-weight,  for  the  last  four  months 
of  the  experiment  showed  an  average  daily  katabolism  of  7.45 
grams  of  nitrogen,  corresponding  to  a  breaking  down  of  46.5 
grams  of  proteid  material  daily.  Yet,  with  this  low  rate  of 
proteid  exchange,  he  maintained  his  position  on  the  team  with 
satisfaction  to  all,  and  with  the  consciousness  of  improved 
physical  condition  and  greater  freedom  from  fatigue.  Other 
subjects,  as  the  laboratory  workers  of  the  professional  group, 
observed  that  the  customary  late  afternoon  fatigue,  coincident 
with  the  continued  walking  and  standing  about  the  laboratory, 
gradually  became  far  less  conspicuous  than  usual;  so  that 
there  seemed  to  be  a  consensus  of  opinion  that  in  some  way 
the  change  in  diet  was  conducive  to  greater  freedom  from 
muscular  weariness. 

It  is  well  understood  by  physiologists  that  the  ability  of 
a  muscle  to  do  work  is  inhibited  by  any  condition  that  tends 
to  depress  the  general  nutritive  state  of  the  body,  or  that 
interferes  with  the  local  nutrition  of  the  muscle  or  muscles 
involved.  On  the  other  hand,  there  are  certain  well-recognized 
conditions  that  tend  to  augment  the  power  of  the  muscle, 
notably  an  increased  circulation  of  blood  through  the  tissue, 
the  taking  of  food,  and  especially  the  introduction  of  sugar. 
Further,  experiments  have  shown  that  when  a  given  set  of 
muscles  has  been  made  to  work  excessively,  other  muscles  of 
the  body  quite  remote  will  share  in  the  fatigue,  thus  implying 
that  muscular  weariness  and  the  diminished  power  to  do  work 
are  connected  with  what  may  be  termed  fatigue  products, 
which  are  distributed  by  means  of  the  circulation.  In  this 
way,  muscles  and  nerve  endings  alike  are  exposed  to  the 
inhibitory  influence  of  waste  products  of  unknown  composi- 


TRUE  FOOD  REQUIREMENTS  209 

tion,  formed  in  the  muscle,  and  as  previously  stated,  we  may 
conceive  of  an  exaggerated  exogenous  katabolism,  with  exces- 
sive proteid  intake,  by  which  muscular  fatigue  and  weariness 
may  be  augmented ;  hence,  the  beneficial  effect  in  this  direction 
of  a  more  rational  food  consumption,  by  which  proteid  katabol- 
ism shall  be  reduced  to  a  true  physiological  level. 

With  these  marked  effects  on  strength  and  fatigue,  it  is 
reasonable  to  assume  that  some  corresponding  action  may  be 
exerted  on  physical  endurance.  As  is  well  known,  strength 
and  endurance,  though  related,  are  quite  distinct  and  can  be 
separately  measured.  Strength  tests,  however,  as  usually 
carried  out  in  gymnasium  work,  do  involve  in  considerable 
degree  the  question  of  endurance,  since  it  is  customary  to  use 
as  one  of  the  factors  in  estimating  total  strength  the  number 
of  times  the  man  can  pull  up,  or  push  up,  his  body  on  the 
parallel  bars.  Strictly  speaking,  however,  the  strength  of 
a  muscle  is  measured  by  the  maximum  force  it  can  exert  in  a 
single  contraction,  while  its  endurance  is  estimated  from  the 
number  of  times  it  can  contract  well  within  the  limit  of  its 
strength. 

It  is  well  known  that  endurance,  both  physical  and 
mental,  is  one  of  the  most  variable  of  the  human  faculties, 
and  it  is  usually  considered  that  exercise  or  training  is  the 
chief  cause  of  the  differences  so  frequently  seen.  The  Maine 
guide  will  row  a  boat  or  paddle  a  canoe  for  the  entire  day 
without  undue  fatigue,  while  the  novice,  though  he  may  have 
the  necessary  strength,  lacks  the  endurance  to  continue  the 
task  longer  than  a  few  hours.  As  expressed  by  Professor 
Fisher,  "  Some  persons  are  tired  by  climbing  a  flight  of  stairs, 
whereas  the  Swiss  guides,  throughout  the  summer  season,  day 
after  day  spend  the  entire  time  in  climbing  the  Matterhorn 
and  other  peaks ;  some  persons  are  '  winded '  by  running  a 
block  for  a  street  car,  whereas  a  Chinese  coolie  will  run  for 
hours  on  end ;  in  mental  work,  some  persons  are  unable  to 

14 


210  THE  NUTRITION  OF  MAN 

apply  themselves  more  than  an  hour  at  a  time,  whereas 
others,  like  Humboldt,  can  work  almost  continuously  through 
eighteen  hours  of  the  day."  Again,  Fisher  states  that 
"  among  some  75  tests  of  different  persons  holding  their  arms 
horizontal,  many  were  found  whose  arms  actually  dropped 
against  their  will  inside  of  10  minutes,  whereas  several  were 
able  to  hold  them  up  over  1  hour,  and  one  man  held  them  3 
hours  and  20  minutes,  or  a  round  200  minutes,  and  then 
dropped  them  voluntarily.  Similarly  with  deep  knee-bending, 
some  persons  were  found  physically  unable  to  rise  again  from 
the  stooping  posture  after  accomplishing  less  than  500  bend- 
ings,  whereas  several  succeeded  in  stooping  1000  times,  and  in 
one  case,  2400.  "  Here,  we  have  inherent  differences  in  endur- 
ance not  associated  with  training  or  exercise,  and  the  question 
may  well  be  asked,  What  is  the  cause  of  these  radical  variations 
in  the  ability  to  repeat  a  simple  muscular  exertion  ? 

Hitherto,  little  attention  has  been  paid  to  the  possible  influ- 
ence of  diet  upon  this  faculty.  It  has  always  been  assumed 
that  endurance,  like  physical  strength,  is  augmented  by  a  rich 
proteid  diet,  but  it  has  never  been  considered  that  diet  by  itself 
was  a  factor  of  any  great  moment  as  compared  with  training  or 
persistent  exercise.  It  is  true  that  claims  have  been  advanced 
from  time  to  time  concerning  the  beneficial  effects  on  endur- 
ance of  a  vegetable  diet,  and  vegetarians  have  frequently  pre- 
sented glowing  reports  of  the  great  increase  in  endurance  they 
have  experienced,  but  little  attention  has  been  given  to  such 
statements,  and  the  matter  has  remained  more  or  less  in 
obscurity. 

Recently,  Professor  Irving  Fisher,1  of  Yale,  has  conducted 
an  interesting  experiment  on  the  influence  of  a  change  in 
diet  on  endurance,  having  the  co-operation  of  nine  healthy 


1  Through  the  kindness  of  Professor  Fisher,  the  writer  lias  had  the  opportu- 
nity of  reading  the  report  of  this  work,  which  at  this  writing  is  not  published, 
a;id  he  has  drawn  upon  it  freely  for  the  following  statements  of  fact. 


TKUE  FOOD   [REQUIREMENTS  211 

students  as  subjects.  The  experiment  extended  through  five 
months,  with  endurance  tests  at  the  beginning,  middle,  and  end 
of  the  period.  At  the  outset,  the  men  consumed  daily  an 
average  of  2880  calories,  of  which  210  were  in  the  form  of 
flesh  foods,  such  as  meats,  poultry,  fish  and  shell-fish;  2.6 
calories  of  proteid  being  ingested  for  each  pound  of  body- 
weight.  At  the  close  of  the  experiment,  the  per  capita  calo- 
ries had  fallen  to  2220,  of  which  only  30  were  in  flesh 
foods,  and  the  proteid  had  fallen  to  1.4  calories  per  pound  of 
body-weight.  In  other  words,  the  total  calories  of  the  daily 
ration  had  dropped  off  about  25  per  cent,  the  proteid  about  40 
per  cent,  and  the  flesh  foods  over  80  per  cent,  or  to  about  one- 
sixth  of  their  original  amount. 

To  determine  the  endurance  of  the  subjects,  six  simple 
gymnastic  tests  were  employed,  and  one  of  mental  endurance. 
The  physical  tests  consisted  of  (1)  in  rising  on  the  toes  as 
often  as  possible ;  (2)  deep  knee-bending,  or  stooping  as  far 
as  possible  and  rising  to  the  standing  posture,  repeating 
as  often  as  possible  ;  (3)  while  lying  on  the  back,  raising 
the  legs  from  the  floor  to  a  vertical  position  and  lower- 
ing them  again,  repeating  to  the  point  of  physical  exhaus- 
tion; (4)  raising  a  5-lb.  dumb-bell  (with  the  triceps)  in  each 
hand  from  the  shoulder  up  to  the  highest  point  above  the 
head,  repeating  to  the  point  of  physical  exhaustion;  (5) 
holding  the  arms  from  the  sides  horizontally  for  as  long  a 
time  as  possible ;  (6)  raising  a  dumb-bell  (with  the  biceps) 
in  one  hand  from  a  position  in  which  the  arm  hangs  free, 
to  the  shoulder  and  back,  repeating  to  the  point  of  physical 
exhaustion.  This  test  was  taken  with  four  successive  dumb- 
bells of  decreasing  weight,  viz.,  50,  25,  10,  and  5  pounds 
respectively.  The  mental  test  consisted  in  adding  specified 
columns  of  figures  as  rapidly  as  possible,  the  object  being  to 
find  out  whether  the  rapidity  of  performing  such  work  tended 
to  improve  during  the  experiment. 


212 


THE  NUTRITION  OF  MAN 


The  following  table  shows  the  results  of  the  three  sets  of 
physical  tests  made  in  January,  March,  and  June : 


TESTS  OF  PHYSICAL  ENDURANCE  WITH  THE  NINE  SUBJECT 


Time. 

B. 

E. 

Lq. 

Lw. 

M. 

P. 

B. 

T. 

W. 

1.  Rising  on 

Jan. 

300 

1007 

333 

69 

127 

1482 

702 

900 

1263 

toes 

Mar. 

400 

1265 

2620 

65 

400 

831 

1500 

June 

600 

1061 

3000 

85 

1500 

1800 

1263 

1800 

3350 

2.  Deep  knee- 

Jan. 

82 

142 

70 

48 

132 

208 

374 

129 

404 

bending 

Mar. 

191 

47 

June 

200 

81 

202 

58 

156 

230 

453 

250 

608 

3.  Leg 

Jan. 

25 

62 

9 

22 

30 

27 

50 

23 

30 

raising 

Mar. 

33 

34 

40 

June 

33 

38 

20 

35 

31 

37 

103 

19 

63 

4.  51b. 

Jan. 

75 

138 

78 

38 

51 

44 

100 

83 

185 

Dumb-bell 

Mar. 

106 

(triceps) 

June 

127 

59 

80 

61 

76 

56 

104 

101 

501 

m.  B. 

m.  i. 

m.  •. 

m.  •. 

m.  a. 

m.  •. 

m.  a. 

m.  8, 

m.    •. 

5.  Holding 

Jan. 

6-0 

1-33 

4-7 

3-37 

3-30 

5-39 

2-6 

3-22 

11-0 

arms  hori- 

Mar. 

5-49 

15-35 

zontal 

June 

9-36 

2-66 

3-60 

3-0 

6-6 

10-1 

3-16 

3-24 

23-45 

6.  251b. 

Jan. 

60 

18 

16 

6 

20 

11 

10 

25 

64 

Dumb-bell 

June 

105 

10 

26 

33 

30 

29 

27 

76 

108 

(biceps) 

The  data  presented  show  a  marked  improvement  in  March 
and  June  over  the  record  made  at  the  beginning  of  the  exper- 
iment in  January,  except  in  the  case  of  one  subject,  E.  As 
Fisher  states,  the  increased  endurance  observed  can  be  as- 
cribed only  to  dietetic  causes,  since  no  other  factors  of  known 
significance  could  have  aided  in  the  result.  The  dietetic 
changes,  as  we  have  seen,  consisted  in  a  slight  reduction  of 
the  total  amount  of  food  consumed  daily,  but  with  a  large 
reduction  of  the  proteid  element,  especially  from  flesh  foods. 
It  is  significant,  says  Fisher,  that  the  only  man  whose 
strength  and  endurance  showed  any  decrease  was  E,  "whose 


TRUE  FOOD  REQUIREMENTS  213 

case  was  exceptional  in  almost  all  respects.  His  reduction 
in  quantity  of  food,  except  for  a  spurt  at  the  end,  was 
less  than  of  most  of  the  men ;  his  reduction  in  proteid,  with 
the  same  exception,  was  the  least  of  all ;  his  reduction  in 
quantity  of  flesh  foods  was  the  least  of  all."  He  stands  out 
conspicuously  as  the  one  man  whose  endurance  failed  to 
improve.  The  mental  test  carried  out  with  the  subjects 
pointed  to  "  a  slight  increase  in  mental  quickness,"  but  the 
adding  test  was  too  short  to  be  of  great  value. 

We  see  in  these  results  another  confirmation  of  the  view 
that  the  welfare  of  the  body  is  not  impaired  by  a  marked 
reduction  in  the  amount  of  proteid  food;  on  the  contrary, 
benefit  results  in  the  increased  efficiency  which  manifests 
itself  in  various  directions.  Physical  endurance  is  an  asset 
not  to  be  ignored,  and  like  the  strength  of  an  individual,  it 
may  well  be  fostered  by  the  recognition  and  practice  of 
a  principle  which  seemingly  has  a  firm  physiological  basis. 
Whether  the  fatigue  poisons  come  from  the  excessive  exoge- 
nous katabolism  of  proteids  in  general,  or  whether  they  are 
derived  directly  in  a  measure  from  flesh  foods,  need  not  be 
considered  here ;  the  main  point  is  that  by  lowering  the  rate 
of  proteid  katabolism,  which  necessarily  compels  a  reduction 
in  the  amount  of  flesh  foods,  there  is  a  diminished  quantity 
of  nitrogenous  waste  floating  about  in  the  body.  Further,  we 
need  not  criticise  too  closely  the  method  by  which  the  reduc- 
tion of  food  is  accomplished ;  whether  it  be  by  encouraging 
mastication,  with  a  view  to  better  tasting  and  fuller  enjoy- 
ment of  the  food,  to  the  point  of  involuntary  swallowing ;  or 
whether  we  follow  natural  taste  and  appetite,  reinforced  by 
the  use  of  reason,  with  a  full  appreciation  of  the  principle 
that  the  welfare  of  the  body  is  best  subserved  by  a  quantity 
of  food  commensurate  with  true  physiological  needs. 

In  making  this  presentation  of  the  true  food  requirements 
of  the  body  as  based  on  the  results  of  physiological  experi- 


214  THE  NUTRITION   OF  MAN 

mentation  and  observation,  I  am  by  no  means  unmindful  of 
the  dangers  of  underfeeding ;  but  this  is  a  condition  compara- 
tively rare.  When  occurring,  as  stated  by  Dr.  Curtis,  "  it  is 
either  because  of  dyspepsia,  in  which  case  it  really  is  involun- 
tary, or  comes  from  some  silly  notion  born  of  a  combination 
of  innate  mental  crookedness  and  that  *  little  knowledge  '  that 
is  a  dangerous  thing."  Overfeeding  is  the  predominant 
dietetic  sin,  and  with  the  prevailing  dietary  standards,  as 
fixed  by  common  usage,  there  is  good  ground  for  believing 
that  it  will  continue  for  many  years  to  come.  Reason  tells 
us,  however,  in  the  practice  of  our  personal  nutrition,  to  steer 
a  middle  course  between  physiological  excess  on  the  one  side, 
and  the  minimal  food  requirement  on  the  other.  To  quote 
again  from  Dr.  Curtis,1  who  has  expressed  the  matter  very 
forcibly,  "  The  physiological  chemist  can  easily  draw  a  line 
on  the  Scylla  (starvation)  side  of  the  channel.  A  dietary 
whereby  the  system  gets  less  than  it  pays  out  is,  obviously,  a 
dangerous  veer  toward  starvation  rock.  But  on  the  Charybdis 
(stuffing)  side,  just  as  the  whirlpool  itself  has  no  well-defined 
border,  the  channel  boundary  is  not  so  easily  marked.  The 
case  is  exactly  analogous  to  the  stoking  of  a  furnace.  The 
proportion  of  ash  to  live  coals  is  a  telltale  as  to  underfeeding, 
but  not  as  to  overfeeding.  With  undersupply  of  fuel  the 
ashes  overbalance  the  live  coals,  and  the  fire  is  thus  foretold 
to  be  going  out.  But  with  an  oversupply  the  fire  simply 
burns  the  faster :  all  the  fuel  continues  to  be  consumed ;  the 
more  coal  simply  makes  the  more  ash,  so  that  equilibrium  is 
not  disturbed,  although  maintained  at  a  higher  level.  To 
argue,  therefore,  that  a  given  dietary  is  none  too  large,  because 
the  balance  between  the  material  receipts  and  expenditures  of 
the  economy  is  not  upset,  would  be  like  saying  that  a  given 


1  Edward  Curtis,  M.  D. :  Nature  and  Health.    New  York,  Henry  Holt  &  Co. 
1906.    p.  71. 


TKUE  FOOD   KEQUIKEMENTS  215 

furnace-fire  is  certainly  none  too  hot,  since  the  ashes  raked 
out  of  the  fire-box  just  correspond  to  the  amount  of  coal 
shovelled  in.  The  same  would  be  equally  true  of  a  slower 
fire  consuming  much  less  fuel.  The  philosophy  of  the  matter 
is,  then,  to  find  the  minimum  of  steam  that  will  run  the 
engine,  and  then  maintain  a  fire  somewhat  hotter  than  the 
exact  requirement,  in  order  to  run  no  risk  of  failure;  or, 
to  return  to  the  metaphor  already  employed,  the  would-be 
careful  liver  must  simply  note  how  close  to  Scylla  other 
voyagers  have  sailed  with  safety,  and  then  steer  his  own  bark 
accordingly." 

As  one  looks  through  the  many  careful  dietary  studies  that 
have  been  made  in  recent  years,  it  is  easy  to  find  striking 
illustrations  of  people,  and  communities  of  people,  who  have 
lived  for  long  periods  of  time  on  dietaries  so  strikingly  simple 
and  meagre  that  it  seems  difficult  at  first  glance  to  believe 
their  daily  needs  could  have  been  entirely  satisfied.  Yet,  such 
observations  are  quite  in  accord  with  the  facts  we  have  been 
presenting,  and  they  afford  additional  evidence  that  the  arti- 
ficial dietary  standards  that  have  been  set  up  are  widely  at 
variance  with  the  real  requirements  of  the  body  for  food.  It 
may  be  quite  true  that  many  of  the  people  referred  to  have 
been  and  are  faddists,  with  peculiar  notions  regarding  food, 
based  on  religious  or  other  scruples,  but  that  has  no  bearing 
on  the  main  contention  that  they  have  lived  for  many  years 
on  amounts  of  food  ridiculously  small  as  compared  with  the 
ordinary  customs  of  mankind.  Thus,  in  Professor  Jaffa's 
report l  of  investigations  made  among  fruitarians  and  Chinese 
of  California  is  an  interesting  account  of  a  dietary  study  of  a 
family  of  fruitarians,  consisting  of  two  women  and  three 
children.  They  had  all  been  fruitarians  from  five  to  seven 
years,  their  diet  being  limited  to  nuts  and  fruit,  except  for 


1  Bulletin  No.  107,  Office  of  Experiment  Stations,  U.  S.  Department  of  Agri- 
culture, 1901,  from  which  the  descriptions  given  have  been  taken. 


216  THE  NUTRITION  OF  MAN 

the  addition  of  celery,  honey,  olive  oil,  and  occasionally  a 
small  amount  of  prepared  cereal  food.  This  family  was  in 
the  habit  of  taking  only  two  meals  a  day ;  at  10.30  in  the 
morning  and  at  5  o'clock  in  the  afternoon.  The  first  meal 
always  consisted  of  nuts  and  fruit,  the  nuts  being  eaten  first. 
At  the  second  meal,  nuts  were  usually  replaced  by  olive  oil 
and  honey.  The  nuts  made  use  of  were  almonds,  Brazil 
nuts,  pine  nuts,  pignolias  (a  variety  of  pine  nuts),  and  wal- 
nuts. Fruits,  both  fresh  and  dried,  were  used,  the  former 
including  apples, apricots,  bananas,  figs,  grapes,  olives  (pickled), 
oranges,  peaches,  pears,  plums,  and  tomatoes.  The  dried  fruits 
were  dates  and  raisins. 

On  this  limited  dietary  of  raw,  uncooked  food,  with  a  com- 
plete absence  of  the  high-proteid  animal  foods,  and  the  ordi- 
nary vegetables,  legumes,  etc.,  and  without  eggs  or  milk,  this 
family,  with  three  growing  children,  had  lived  all  these  years. 
Note  now  what  Jaffa  observed  regarding  their  food  consump- 
tion. The  first  subject,  a  woman  33  years  of  age  and  weigh- 
ing 90  pounds,  was  studied  for  twenty  consecutive  days,  all 
the  food  eaten  being  carefully  weighed  and  its  chemical  com- 
position determined.  As  a  result,  it  was  found  that  the  aver- 
age amount  of  food  consumed  per  day  was:  proteid,  33 
grams ;  fat,  59  grams ;  carbohydrate,  150  grams ;  with  a  total 
fuel  value  of  1300  calories.  The  other  members  of  the  family 
were  studied  in  a  similar  manner,  one  of  the  children  being 
the  subject  on  two  separate  occasions.  The  table  (on  page 
217),  showing  the  average  daily  food  consumption,  gives  a 
summary  of  the  results  obtained. 

As  Professor  Jaffa  states,  the  tentative  dietary  standard  for 
a  woman  at  light  work  calls  for  90  grams  of  proteid  daily, 
with  a  fuel  value  of  2500  calories.  Both  of  these  women 
were  light  in  weight,  and  furthermore  had  no  occasion  to  do 
much  physical  work ;  but  even  so,  a  daily  consumption  of  only 
0.8  gram  and  0.52  gram  of  proteid,  respectively,  per  kilo  of 


TRUE  FOOD  REQUIREMENTS 


217 


Proteid. 

Fat. 

Carbo- 
hydrate. 

Fuel 
Value. 

Proteid 
per  Kilo 
Body- 
weight. 

grama 

grams 

grams 

calories 

grams 

Woman,  33  years  old, 

Weight  90  Ibs.  (40.9  kilos)     .     . 

33 

59 

150 

1300 

0.80 

Woman,  #0  years  old, 

Weight  104  Ibs.  (47.3  kilos)   .     . 

25 

57 

90 

1040 

0.52 

Girl,  13  years  old, 

Weight  75J  Ibs.  (34.3  kilos)    .     . 

26 

52 

157 

1235 

0.75 

Boy,  9  years  old, 

Weight  43  Ibs.  (19.5  kilos)     .    . 

27 

56 

152 

1255 

1.38 

Girl,  6  years  old, 

Weight  30i  Ibs.  (13.9  kilos)   .     . 

24 

58 

134 

1190 

1.72 

Girl,  7  years  old, 

Weight  34  Ibs.  (15.4  kilos)     .     . 

40 

72 

134 

1385 

2.59 

body-weight,  with  the  small  calorific  values  indicated,  repre- 
sents a  phenomenally  small  amount  of  food.  And  yet  Jaffa,  in 
referring  to  the  woman  with  the  lowest  intake  of  food,  states 
that  even  this  small  quantity  of  food,  judging  from  the  ap- 
pearance and  manner  of  the  subject,  "seemed  sufficient  for 
her  needs,  enabling  her  to  do  her  customary  housework  and 
take  care  of  her  two  nieces  and  nephew."  Regarding  the 
children,  it  is  stated  that  the  commonly  accepted  American 
dietary  standard  for  a  child  13  years  old  and  of  an  average 
activity  calls  for  about  90  grams  of  proteid  and  2450  calories. 
As  is  seen  from  the  table,  however,  the  13-year-old  girl 
consumed  of  proteid  less  than  one-third,  and  of  fuel  value 
only  about  60  per  cent  of  the  amount  called  for ;  yet,  says 
Jaffa,  u  notwithstanding  the  facts  brought  out  by  this  com- 
parison, the  subject  had  all  the  appearances  of  a  well-fed 
child  in  excellent  health  and  spirits." 

We  need  not  consume  time  in  discussing  the  details  of  this 
experimental  study,  though  the  facts  are  interesting  and  sug- 
gestive, for  it  is  only  the  general  question  of  proteid  require- 
ment and  calorific  value  that  has  interest  for  us  at  present. 
The  fact  is  perfectly  clear  that  this  family  of  fruitarians, 
young  and  old,  were  quite  able  to  live  and  thrive  on  a 


218  THE  NUTRITION   OF  MAN 

diet,  the  value  of  which  in  proteid  and  calories  was  at  as 
low  a  level  as  was  attained  in  our  experimental  studies. 
The  rock  of  starvation,  however,  was  not  touched  or  even 
sighted  by  the  voyagers  down  this  stream  of  nutrition. 
We  may  all  agree  that  it  would  be  preferable,  as  a  rule, 
to  acquire  the  proteids,  fats,  and  carbohydrates  of  our  diet 
from  a  greater  variety  of  sources  than  did  the  fruitarians ;  we 
might  well  complain  at  a  dietary  so  limited  in  quality ;  but 
the  point  to  be  emphasized  is  that  the  low  intake  of  proteid 
and  the  low  fuel  value  were  quite  adequate  for  meeting  the 
needs  of  the  body.  "  It  is  a  difficult  matter,"  says  Professor 
Jaffa,  "  to  draw  any  general  conclusions  from  the  foregoing 
dietaries  without  being  unjust  to  the  subjects.  It  would  ap- 
pear, upon  examining  the  recorded  data  and  comparing  the  re- 
sults with  commonly  accepted  standards,  that  all  the  subjects 
were  decidedly  undernourished,  even  making  allowances  for 
their  light  weight.  But  when  we  consider  that  the  two  adults 
have  lived  upon  this  diet  for  seven  years,  and  think  they  are 
in  better  health  and  capable  of  more  work  than  they  ever 
were  before,  we  hesitate  to  pronounce  judgment.  The  three 
children,  though  below  the  average  in  height  and  weight,  had 
the  appearance  of  health  and  strength.  They  ran  and  jumped 
and  played  all  day  like  ordinary  healthy  children,  and  were 
said  to  be  unusually  free  from  colds  and  other  complaints 
common  to  childhood." 

Turning  now  to  a  larger  community,  —  the  island  nation  of 
Japan,  —  whose  exploits  in  war  have  recently  attracted  the 
attention  of  the  civilized  world,  we  find  a  people  the  great 
majority  of  whom  have  remained  untouched  by  the  prodigality 
of  western  civilization,  and  whose  customs  and  habits  still  bear 
the  imprint  of  simplicity  and  frugality.  After  the  restoration 
of  Japan  and  the  reorganization  of  the  government  in  1867, 
much  attention  was  directed  to  the  methods  of  living  and  to 
the  dietary  habits  of  the  people,  with  the  result  that  during 


TKUE  FOOD  REQUIREMENTS 


219 


the  last  twenty-five  years  there  have  been  slowly  accumu- 
lating many  important  data  bearing  on  the  food  consumption 
of  the  people.  These  have  recently  been  brought  together  in 


Subjects. 

Body- 
weight. 

Digestible  Nutrients  and  Energy  per  Man 
per  Day. 

Proteid. 

Fat. 

Carbo- 
hydrate. 

Fuel 
Value. 

School  business  agent  .    . 
Physician   

kilos 

57.5 

47.6 
49.0 

grams 

65.3 
61.9 
81.5 
74.8 

grams 

11.3 

8.0 
19.6 
11.2 

grams 
493.8 

468.5 
366.2 
326.9 

calories 
2467 

2315 
2082 
1811 

Medical  student  .... 

Medical  student  .... 

48.5 

64.7 

5.1 

469.6 

2305 

Military  cadets    .... 



72.3 

11.7 

618.1 

3021 

Prisoners  without  work    . 

47.6  A 

36.3 

5.6 

360.4 

1726 

Prisoners  at  light  work     . 

48.01 

43.1 

6.2 

443.9 

2112 

Prisoners  at  hard  work     . 

40.2 
40.5 

56.7 
48.3 
46.5 

7.5 
15.5 
19.7 

610.8 
438.2 
485.3 

2884 
2201 
2430 

Hygienic  assistant  .     .     . 

Medical  student  .... 

51.0 

42.8 

14.0 

438.2 

2163 

Police  prisoners  .... 

.... 

42.7 

8.7 

387.3 

1896 

Army  surgeon     .... 
Soldier    

54.0 
66.7 
61.0 

56.7 

79.3 
75.8 
58.8 
65.2 

11.7 
13.5 
11.3 
10.9 

502.0 
563.8 
467.8 
459.6 

2567 
2828 
2330 
2276 

Soldier    

Soldier    

an  interesting  volume  by  Kintaro  Oshima,  and  published 2  in 
the  English  language. 

As  is  well  known,  the  great  majority  of  the  people  of  Japan 

1  Average  weight  of  twenty  subjects. 

2  A  Digest  of  Japanese  Investigations  on  the  Nutrition  of  Man.    Bulletin 
No.  159,  Office  of  Experiment  Stations,  U.  S.  Department  of  Agriculture,  1905. 


220  THE  NUTRITION  OF  MAN 

live  mainly  on  a  vegetable  diet.  It  is  also  known  to  physi- 
ologists at  least  that  Japanese  dietaries  are  characterized  by 
a  relatively  small  amount  of  proteid,  though  since  the  pas- 
sage of  the  Food  Supply  Act  of  the  navy  in  1884,  the  proteid- 
content  of  the  navy  ration  has  been  decidedly  increased.  Ifc 
will  be  interesting  to  note  a  few  of  the  results  collated  by 
Oshima,  and  some  of  the  conclusions  that  he  draws  from  the 
data  presented.  The  foregoing  table  shows  a  few  of  the  more 
striking  results  of  the  dietary  studies  obtained  with  various 
classes  of  people,  where  the  food  used  was  largely  vegetable, 
but  generally  with  some  admixture  of  fish  or  meat. 

The  figures  presented,  which  represent  the  actual  amounts  of 
food  consumed,  with  proper  correction  for  the  indigestible  por- 
tion, show  a  much  smaller  intake  of  proteid  than  is  common 
with  European  and  American  people ;  indeed,  both  proteid  and 
fuel  value  are  very  much  less  than  common  practices  call  for 
among  western  peoples,  even  when  due  allowance  is  made  for 
differences  in  body-weight.  To  quote  from  Oshima,  "  Prob- 
ably the  most  interesting  of  the  dietary  studies  are  those  with 
poorer  classes,  which  comprise  by  far  the  larger  part  of  the 
population.  The  dietaries  of  the  miscellaneous  class,  includ- 
ing employees,  prisoners,  etc.,  consisted  largely  of  vegetable 
foods  and  supplied  on  an  average  59  grams  of  proteid  and 
2190  calories  of  energy  per  man  per  day."  Especially  sug- 
gestive were  the  results  of  a  study  made  with  a  military 
colonist,  a  type  of  man  very  common  in  Japan ;  in  reality 
farmers  who  live  at  home,  but  have  military  drill  at  certain 
fixed  times.  The  subject  was  carefully  selected  under  advice 
of  officers  in  charge  of  the  district,  and  weighed  59.9  kilo- 
grams. His  diet  consisted  solely  of  cereals  and  vegetables, 
being  identical  with  that  of  the  people  in  the  rural  districts  of 
Japan.  His  daily  food  was  found  to  be  composed  of  46.3  grams 
of  digestible  proteid,  with  a  fuel  value  of  2703  calories. 

Even  more  striking  were  the  results  obtained  in  a  study  of 


TEUE   FOOD  REQUIREMENTS 


221 


the  dietary  habits  of  three  healthy  natives  of  Formosa,  em- 
ployed as  day  laborers  at  the  military  hospital.  They  weighed 
respectively  60.9,  55,  and  54.8  kilograms.  The  main  portion 
of  their  diet  was  rice,  supplemented,  however,  by  a  little  salt 
fish,  salted  melon,  spinach,  ginger,  and  greens.  The  daily 
amount  of  proteid  ingested  was  48.0  grams  (37.4  grams  of 
digestible  proteid),  with  a  total  fuel  value  of  1948  calories. 
A  composite  sample  of  urine  covering  seven  days  showed  an 
average  daily  output  of  metabolized  nitrogen  of  6.93  grams, 
corresponding  to  a  breaking  down  of  43.3  grams  of  proteid. 

Especially  interesting  also  is  a  series  of  experiments  with 
professional  men,  reported  by  Oshima,  in  which  attention  was 
paid  to  nitrogen  balance.  The  following  table  shows  the 
essential  results: 


Subject. 

Body- 
weight. 

Character 
of  Food. 

Digestible  Nutrients  and  Energy  per  Man  per  Day. 

Proteid. 

Fat. 

Carbo- 
hydrate. 

Fuel 
Value. 

Nitrogen 
Balance. 

N.  K. 

kilos 

mixed  diet 

grams 
72.7 

grams 
18.3 

grams 

380.7 

calories 
2091 

+ 

S.  A. 

49.5 

mixed  diet 

69.8 

20.2 

410.7 

2222 

+ 

N.  K. 

42.9 

mixed  diet 

64.4 

8.5 

396.3 

2028 

+ 

N.  K. 

43.2 

mixed  diet 

62.8 

K7 

433.2 

2178 

+ 

N.  K. 

43.0 

vegetable 

68.5 

19.7 

433.0 

2303 

+ 

N.  K. 

43.9 

vegetable 

36.8 

6.6 

381.0 

1824 

- 

N.  K. 

42.4 

vegetable 

40.6 

8.7 

462.6 

2200 

+ 

S.  A. 

49.6 

vegetable 

34.4 

7.5 

451.9 

2119 

- 

S.  A. 

49.9 

vegetable 

43.5 

9.1 

500.0 

2376 

-I- 

It  is  to  be  observed  that  in  all  of  the  above  experiments, 
excepting  two,  the  subjects  gained  nitrogen  even  with  the  low 
proteid  intake  and  the  small  fuel  value  of  the  day's  food. 
Particularly  noteworthy,  in  harmony  with  previous  state- 


222  THE  NUTRITION  OF  MAN 

ments,  are  the  results  of  the  sixth  and  seventh  experiments. 
In  the  sixth  experiment,  the  subject  was  not  able  to  maintain 
nitrogen  equilibrium  on  a  diet  containing  36.8  grams  of  diges- 
tible proteid  and  having  a  fuel  value  of  1825  calories,  but  by 
raising  the  intake  of  carbohydrate  food  (seventh  experiment)  to 
462  grams  daily,  thereby  increasing  the  fuel  value  of  the  daily 
ration  to  2200  calories  (with  a  slight  increase  in  the  proteid 
incidental  thereto),  the  body  was  able  to  change  its  previous 
loss  of  nitrogen  into  a  gain ;  in  other  words,  the  added  car- 
bohydrate served  as  a  protector  of  proteid. 

The  series  of  experiments  as  a  whole,  however,  is  to  be  con- 
sidered in  the  light  of  additional  data  bearing  on  the  dietary 
customs  of  a  people  who  for  generations  have  apparently  lived 
and  thrived  on  a  daily  ration  noticeably  low  in  its  content  of 
proteid,  as  well  as  low  in  its  calorific  value.  As  Oshima 
states,  "  It  is  probably  fair  to  infer  that  the  amount  of  pro- 
teid in  the  dietaries  of  the  classes  living  largely  on  vegetable 
foods  (and  they  constitute  the  larger  part  of  the  population) 
may  not  be  very  far  from  60  grams  per  day,"  or  45  grams  of 
digestible  proteid.  It  is  reasonable  to  assume  tha*  the  people 
live  in  this  way  from  force  of  habit  or  of  necessity,  and  we 
may  agree  with  Baelz,  a  professor  connected  with  the  medical 
faculty  of  Tokyo  University,  "  that  their  diet  is  sufficient 
from  a  physiological  standpoint."  Doubtless  a  mixed  diet, 
with  a  larger  proportion  of  animal  food,  did  their  means 
readily  permit,  would  offer  some  advantages  from  the  stand- 
point of  palatability  and  variety,  but  it  is  questionable  if  any 
material  gain  in  health  or  strength  would  result.  "It  is 
sometimes  remarked,"  says  Oshima,  "  that  the  peasants  in 
the  rural  districts  of  Japan,  living  largely  on  vegetable  food, 
are  really  healthier  and  stronger  than  people  of  the  better 
classes,  who  live  on  a  mixed  diet,  and  the  better  physical 
condition  of  the  former  is  commonly  believed  to  be  due  to 
their  diet."  This,  however,  is  a  difficult  matter  to  decide, 


TRUE  FOOD  REQUIREMENTS  223 

since  there  are  so  many  other  factors  that  are  liable  to  play  a 
part,  such  as  the  general  conditions  of  life  which  are  so  widely 
different  in  the  two  classes. 

It  is  plainly  evident  that  the  daily  diet  of  the  great  bulk 
of  the  Japanese  people  has  been  characterized  by  a  very  low 
proteid  standard,  as  contrasted  with  the  standards  and  usages 
of  the  majority  of  European  and  American  people.  The  fact 
is  brought  forward  merely  as  confirmatory  evidence,  on  a 
large  scale,  of  the  perfect  safety  of  lowering  the  consumption 
of  proteid  food  to  somewhere  near  the  level  of  the  physiolog- 
ical requirements  of  the  body.  Generations  of  low  proteid 
feeding,  with  the  temperance  and  simplicity  in  dietary  matters 
thereby  implied,  have  certainly  not  stood  in  the  way  of  phe- 
nomenal development  and  advancement  when  the  gateway 
was  opened  for  the  ingress  of  modern  ideas  from  western 
civilization.  Many  changes  are  sure  to  follow  in  the  foot- 
steps of  the  nation's  progress,  and  among  these  it  is  safe  to 
prophesy  that  as  public  and  private  wealth,  and  resources  in 
general,  increase,  the  dietary  of  the  people  will  gradually 
assume  a  more  varied  character  with  corresponding  increase 
in  volume.  Whether  such  a  change  will  prove  of  real  benefit 
to  the  race,  time  alone  can  determine. 

Having  said  so  much  concerning  the  Japanese,  it  is  proper 
that  a  few  additional  statements  should  be  made.  The 
stature  and  general  physique  of  the  people  could  be  advan- 
tageously improved.  Is  this  a  question  of  dietary,  or  is  it 
connected  with  some  condition  of  life  on  which  the  daily  food 
has  no  bearing ;  or  is  it,  perchance,  a  racial  characteristic  so 
deeply  ingrained  that  conditions  of  environment  are  without 
noticeable  influence?  These  questions  cannot  be  definitely 
answered  at  present.  Finally,  we  may  call  attention  to  the 
dietary  changes  inaugurated  in  recent  years  in  connection 
with  the  new  organization  of  the  imperial  army  and  navy. 
With  a  view  to  increasing  the  efficiency  of  the  men,  following 


224  THE  NUTEITION  OF  MAN 

the  customs  of  other  countries,  an  act  was  passed  increasing 
the  amount  of  proteid  food  in  the  navy  dietary.  Oshima's 
report  of  the  various  steps  token  to  accomplish  this  end,  with 
the  results  that  followed,  is  interesting  in  several  ways. 

"  A  large  part  of  the  rice  was  to  be  replaced  by  bread,  and 
meats  were  to  be  used  liberally.  The  experience,  during  the 
first  year  that  this  ration  was  tried,  indicated  that  bread  and 
meat  could  not  be  advantageously  substituted  immediately  for 
the  rice,  because  most  of  the  marines  were  unaccustomed  to 
these  food  materials  ;  consequently,  a  modification  of  the  ration 
was  introduced  in  1885,  whereby  a  rice-barley  mixture  was 
adopted  in  place  of  the  bread.  Barley  was  considered  at  that 
time  as  a  better  article  of  food  than  rice,  on  account  of  its 
higher  proteid  content,  but  later  investigations  showed  that 
the  digestibility  of  the  nutrients  of  barley  was  small.  In  1886, 
an  effort  was  again  made  to  substitute  bread  for  the  rice-barley 
mixture.  In  1890,  the  ration  allowance  was  reduced  by  one- 
fifth  and  an  amount  of  money  equivalent  to  the  cost  of  the 
reduction  in  diet  was  given  to  each  marine  with  which  to  buy 
accessory  food  according  to  his  own  choice.  In  1898,  the  re- 
duction was  made  one-tenth,  instead  of  one-fifth  as  in  pre- 
vious years.  In  1900,  the  cash  allowance  was  abolished  and  a 
new  ration  adopted."  This  ration  contains  about  150  grams 
of  proteid  (animal  and  vegetable  food)  and  has  a  fuel  value  ol 
over  3000  calories.  In  all  of  these  changes,  the  proportion 
of  rice  was  greatly  reduced. 

Probably,  one  of  the  chief  reasons  why  persistent  efforts 
were  made  to  improve  the  dietary  of  the  navy  was  the  preva- 
lence among  the  men  of  the  disease  known  as  beriberi. 
"  While  no  satisfactory  explanation  as  to  the  cause  of  the 
disease  was  offered,  it  was  generally  believed  that  there  was 
some  very  close  relation  between  the  disease  and  the  rice 
diet "  (Oshima).  During  the  years  1878-1883  inclusive,  nearly 
33  per  cent  of  the  marines  suffered  from  beriberi.  With  the 
adoption  of  the  new  ration  in  1884,  in  which  a  large  part 


TKUE  FOOD  REQUIREMENTS  225 

of  the  rice  was  replaced  by  bread  and  other  articles,  and 
with  better  hygienic  conditions,  this  disease  immediately 
began  to  disappear,  and  during  the  six  years  after  the  adop- 
tion of  the  new  diet  only  16  per  cent  of  the  marines  were 
affected  by  the  disease.  Later  on,  hardly  more  than  two 
or  three  cases  a  year  were  recorded.  Advocates  of  a  high 
proteid  diet  bring  forward  this  illustration  as  an  evidence  of 
the  danger  connected  with  a  lowered  proteid  intake ;  t.  e., 
that  the  nutrition  of  the  body  will  be  impaired  and  diseases 
of  various  sorts  liable  to  follow.  Yet,  Oshima  is  very  careful 
to  state,  "  It  should  be  especially  noted  that  here  no  attempt 
has  been  made  to  indicate  the  cause  of  beriberi  or  the  relation 
between  the  disease  and  the  diet."  That  rice  in  itself  can  be 
a  cause  of  the  disease  is  not  to  be  considered  for  a  moment 
Further,  so  far  as  any  facts  are  concerned,  the  writer  can  see 
no  ground  for  considering  that  a  low  rate  of  proteid  metabo- 
lism has  in  itself  any  direct  connection  with  the  disease. 
From  a  dietary  standpoint,  it  seems  far  more  plausible  to 
assume  that  the  great  restriction  in  variety  of  foods,  so  strik- 
ingly manifest  in  the  dietary  of  the  poorer  people  of  Japan, 
results  in  a  lack  of  some  one  or  more  elements  which  con- 
duces to  the  disease,  just  as  in  scurvy  the  lack  of  fresh 
vegetables  on  long  voyages  was  liable  to  be  followed  by  an 
epidemic  of  this  disease. 

Consider  the  natural  character  of  the  dietary  of  the  great 
bulk  of  the  Japanese  people,  determined  as  it  was  by  adverse 
financial  circumstances.  As  Oshima  states,  "  The  rural  popu- 
lation of  the  interior  depends  very  largely  or  entirely  upon  a 
vegetable  diet.  Fish  is  eaten  perhaps  once  or  twice  a  month, 
and  meat  once  or  twice  a  year,  if  at  all.  The  poorer  working 
classes  in  the  cities  also  use  very  little  animal  food.  But  the 
poorer  classes  in  the  city  and  the  peasantry  of  the  rural 
districts  comprise  nearly  75  per  cent  of  the  total  population, 
and  it  is  therefore  safe  to  assume  that  this  proportion  lives 

15 


226  THE  NUTRITION  OF  MAN 

chiefly,  or  wholly,  upon  vegetable  diet.  And  this,  it  may  be 
observed,  means  vegetarianism  literally.  The  so-called  lacto- 
vegetarianism  is  unknown  in  Japan.  Cows  are  scarce,  and 
milk  and  other  dairy  products  are  expensive,  and  such  as 
are  available  are  consumed  almost  entirely  by  the  wealthier 
people  in  the  cities."  It  is  also  to  be  noted  that  the  amount 
of  fat  in  Japanese  dietaries  is  very  small.  The  reported 
data  indicate  that  the  usual  vegetable  dietaries  contain  only 
about  10  grams  of  fat  per  day,  while  even  in  the  average 
mixed  dietaries  the  amount  rarely  rises  above  20  grams  per 
day.  In  other  words,  the  ordinary  food  of  the  Japanese  was 
characterized  by  great  lack  of  variety,  and  with  such  a  pre- 
ponderance of  carbohydrate  materials  of  a  limited  kind  that 
it  is  easy  to  conceive  of  a  possible  dearth  of  some  essential  or 
accessory  element,  necessary  for  the  preservation  of  that  nutri- 
tive balance  which  aids  in  protection  against  disease. 

If  the  resistance  of  the  body  to  disease  germs  and  toxic 
influences  in  general  is  really  diminished  by  reducing  the 
consumption  of  proteid  food  below  the  set  dietary  stand- 
ards, then  obviously  here  lies  a  tangible  reason  for  the  main- 
tenance of  a  high  proteid  intake.  I  know  of  only  one  series 
of  scientific  observations  that  bears  directly  on  this  question. 
Dr.  Reid  Hunt  of  Washington  has  studied  recently  the  power 
of  resistance  to  the  poison  acetonitrile  of  animals  kept  for 
some  time  upon  a  reduced  proteid  diet.  "My  experiments," 
says  Dr.  Hunt,  "  showed  in  all  cases  that  the  resistance  was 
much  increased."  In  other  words,  the  animals  that  had  been 
fed  a  low  proteid  ration  were  able  to  endure  a  much  larger 
dose  of  the  poison  than  corresponding  animals  on  their  custo- 
mary diet ;  "  they  resisted  2-3  times  the  ordinary  fatal  dose 
of  acetonitrile."  This  general  subject,  however,  is  obviously 
a  very  important  one,  and  merits  further  experimental  study 
under  a  diversity  of  conditions. 

In  conclusion,  the  facts  here  presented  bearing  on  food  re- 


TRUE  FOOD  REQUIREMENTS  227 

quirements,  especially  those  that  relate  to  the  need  for  proteid 
food,  are  seemingly  harmonious  in  indicating  that  the  physio- 
logical necessities  of  the  body  are  fully  met  by  a  much  more 
temperate  use  of  food  than  is  commonly  practised.  Dietary 
standards  based  on  tne  habits  and  usages  of  prosperous  com- 
munities are  not  in  accord  with  the  data  furnished  by  exact 
physiological  experimentation.  Nitrogen  equilibrium  can  be 
maintained  on  quantities  of  proteid  food  fully  fifty  per  cent 
less  than  the  every-day  habits  of  mankind  imply  to  be  neces- 
sary, and  this  without  increasing  unduly  the  consumption  of 
non-nitrogenous  food.  A  daily  metabolism  of  proteid  matter 
equal  to  an  exchange  of  0.10-0.12  gram  of  nitrogen  per  kilo- 
gram of  body-weight  is  quite  adequate  for  physiological 
needs,  provided  a  sufficient  amount  of  non-nitrogenous  foods 
—  fats  and  carbohydrates  —  is  taken  to  meet  the  energy  re- 
quirements of  the  body. 

The  long-continued  experiments  on  many  individuals,  rep- 
resenting different  types  and  degrees  of  activity,  all  agree 
in  indicating  that  equilibrium  can  be  maintained  indefinitely 
on  these  smaller  quantities  of  food,  and  that  health  and 
strength  can  be  equally  well  preserved,  to  say  nothing  of 
possible  improvement.  The  lifelong  experience  of  individu- 
als and  of  communities  affords  sufficient  corroborative  evi- 
dence that  there  is  perfect  safety  in  a  closer  adherence  to 
physiological  needs  in  the  nutrition  of  the  body,  and  that  these 
needs,  so  far  as  proteid  food  is  concerned,  are  in  harmony  with 
the  theory  of  an  endogenous  metabolism,  or  true  tissue  metab- 
olism, in  which  the  necessary  proteid  exchange  is  exceedingly 
limited  in  quantity.  There  are  many  suggestions  of  improve- 
ment in  bodily  health,  of  greater  efficiency  in  working  power, 
and  of  greater  freedom  from  disease,  in  a  system  of  dietetics 
which  aims  to  meet  the  physiological  needs  of  the  body  with- 
out undue  waste  of  energy  and  unnecessary  drain  upon  the 
functions  of  digestion,  absorption,  excretion,  and  metabolism 


228  THE  NUTRITION  OF  MAN 

in  general ;  a  system  which  recognizes  that  the  smooth  run- 
ning of  man's  bodily  machinery  calls  for  the  exercise  of  rea- 
son and  intelligence,  and  is  not  to  be  intrusted  solely  to  the 
dictates  of  blind  instinct  or  to  the  leadings  of  a  capricious 
appetite. 


CHAPTER  VII 

THE  EFFECT  OF  LOW  PKOTEID  DIET  ON  HIGH 
PROTEID  ANIMALS 

TOPICS:  A  wide  variety  of  foods  quite  consistent  with  temperance  in 
diet.  Safety  of  low  proteid  standards  considered.  Arguments  based 
on  the  alleged  effects  of  low  proteid  diet  on  high  proteid  animals. 
Experiments  of  Immanuel  Munk  with  dogs.  Experiments  of  Rosen- 
heim.  Experiments  of  Jagerroos.  Comments  on  the  above  experi- 
ments. The  experiments  of  Watson  and  Hunter  on  rats.  The 
writer's  experiments  with  dogs.  Details  of  the  results  obtained  with 
six  dogs.  Comparison  of  the  results  with  those  of  previous  investiga- 
tors. Effect  of  a  purely  vegetable  diet  on  dogs.  Different  nutritive 
value  of  specific  proteids  considered.  Possible  influence  of  difference 
in  chemical  constitution  of  individual  proteids.  Effect  of  low  proteid 
diet  on  the  absorption  and  utilization  of  food  materials  in  the  intestine 
of  dogs.  General  conclusions  from  the  results  of  experiments  with 
animals. 

MAN  is  by  choice  an  omnivorous  creature ;  he  reaches 
out  ordinarily  in  all  directions  for  as  wide  a  variety 
of  foods  as  his  circumstances  and  surroundings  will  allow.  He 
rightly  cultivates  a  taste  for  foods  that  have  individuality  of 
flavor,  and  derives  pleasure  and  satisfaction  from  the  eating 
of  delicacies  that  appeal  to  palate  and  to  reason.  All  this  he 
can  do  without  becoming  an  epicure  or  a  glutton,  and  without 
violation  of  physiological  laws  or  disregard  of  the  teachings  of 
temperance.  As  a  being  endowed  with  reason  and  intelligence 
he  is,  however,  necessarily  mindful  of  the  possible  deleterious 
effect  of  undue  quantities  of  food,  as  he  is  likewise  mindful  of 
the  desirability  of  avoiding  certain  varieties  of  food  which  per- 
sonal experience  has  taught  him  are  fraught  with  possible 


230  THE  NUTRITION   OF  MAN 

danger.  Care  and  prudence  in  diet  are  legitimate  outcomes 
of  a  reasonable  interest  in  the  welfare  of  the  body,  upon  which 
so  largely  depend  the  happiness  and  working  power  of  the 
individual. 

The  adoption  of  dietary  habits  that  aim  to  accord  with 
the  physiological  requirements  of  the  body  does  not  compel  a 
crucifying  of  the  flesh  or  a  disregard  of  personal  likes  and  dis- 
likes. A  reasonable  intelligence  combined  with  a  disposition  to 
exercise  the  same  degree  of  judgment  and  care  in  the  nutrition 
of  the  body  as  is  expended  on  other  matters,  of  no  greater  im- 
portance, pertaining  to  the  individual,  to  the  household,  or  to 
business  interests,  are  all  that  is  needed  to  bring  about  har- 
mony between  every-day  dietary  habits  and  the  nutritive  re- 
quirements of  the  body.  There  is  no  occasion,  unless  one 
finds  pleasure  and  satisfaction  in  so  doing,  to  resort  to  a  lim- 
ited dietary  of  nuts  and  fruits,  to  become  an  ardent  disciple  of 
vegetarianism,  to  adopt  a  cereal  diet,  to  abjure  meats  entirely, 
or  to  follow  in  an  intensive  fashion  any  particular  dietary 
hobby,  except  so  far  as  may  be  necessary  to  insure  an  ade- 
quate amount  of  non-nitrogenous  foods  to  meet  the  energy 
requirements  of  the  body  without  unduly  increasing  the  in- 
take of  proteid  or  nitrogenous  food.  Naturally,  a  man  leading 
a  life  of  great  physical  activity  with  the  consequent  demand 
for  a  large  energy -yielding  intake  will  be  compelled  to  resort 
largely  to  vegetable  foods,  rich  in  starch  and  poor  in  proteid, 
or  to  eat  largely  of  fatty  foods.  Reliance  on  meats  and  ani- 
mal foods  in  general,  under  such  conditions,  would  plainly 
involve  a  high  proteid  intake  with  a  consequent  high  nitro- 
gen metabolism,  with  the  chance  that  even  then  the  energy 
requirement  would  not  be  fully  met. 

In  view  of  all  that  has  been  said,  reinforced  by  the  various 
facts  brought  forward  as  evidence,  we  must  recognize  the 
value  of  the  non-nitrogenous  foods  as  a  source  of  energy,  and 
this  means  plainly  food  from  the  plant  kingdom.  In  any 


EFFECT   OF  LOW  PKOTEID   DIET  231 

rational  diet,  vegetable  foods  of  low  nitrogen-content  must 
predominate,  while  animal  foods  with  their  higher  nitrogen 
values  must  be  greatly  subordinate  in  amount,  if  the  nitrogen 
or  proteid  metabolism  of  the  body  is  to  be  maintained  at  a 
level  commensurate  with  true  physiological  requirements. 
But  there  comes  the  ever-recurring  question,  Are  the  lower 
proteid  standards  quite  safe  to  follow  ?  Are  we  warranted  in 
turning  aside  from  the  teachings  based  on  the  habits  and 
customs  of  mankind  ?  Many  reasons  have  already  been  pre- 
sented which  seemingly  justify  an  affirmative  answer,  while 
the  experimental  results  and .  the  observations  on  various 
groups  of  people,  covering  years  of  time,  speak  with  no  un- 
certainty regarding  the  element  of  safety,  and  indicate  clearly 
that  the  absolute  proteid  requirement  of  the  body  is  quite 
small ;  much  smaller  indeed  than  the  amount  of  proteid 
food  consumed  by  the  average  individual  would  seemingly 
imply. 

Probably  the  most  striking  evidence,  certainly  of  an  experi- 
mental nature,  so  far  presented  against  the  safety  of  a  rela- 
tively low  proteid  diet  for  man  is  that  based  on  the  results  of 
several  studies  made  to  ascertain  the  effect  of  a  reduced 
proteid  intake  on  so-called  high  proteid  animals.  Animal 
kind  may  be  divided  into  three  groups  according  to  the  nature 
of  their  food,  viz.,  high  proteid  feeders,  such  as  carnivorous 
animals  in  general,  of  which  the  dog  is  a  good  type ;  om- 
nivorous or  moderate  proteid  consumers,  to  which  class  man 
belongs ;  and  low  proteid  consumers,  such  as  herbivorous 
animals.  Three  series  of  experiments  have  been  reported  by 
independent  workers  on  the  effects  of  reducing  the  amount  of 
proteid  food  in  the  diet  of  dogs.  The  results  of  these  experi- 
ments were  of  such  a  character  that  it  has  come  to  be  under- 
stood that  animals  of  this  type  cannot  exist  for  any  great 
length  of  time  on  a  low  proteid  diet.  It  is  affirmed  that  in  a 
relatively  short  period  the  animals  reach  such  a  state  that 


232  THE  NUTRITION  OF  MAN 

they  either  die,  or  are  in  such  poor  condition  that  they  must 
be  fed  a  more  liberal  amount  of  proteid  to  maintain  them 
alive.  The  explanation  offered  is  that  the  low  proteid  diet 
results  u  in  a  loss  of  the  power  of  absorption  from  the  intesti- 
nal tract,  caused  apparently  by  a  change  in  the  condition  of 
the  epithelial  cells,  as  well  as  by  a  diminished  secretion  of  the 
digestive  juices. " 

The  argument  based  on  this  evidence  is  that  while  a  high 
proteid  animal  feels  at  once,  or  almost  immediately,  the  del- 
eterious effect  of  a  reduction  in  the  amount  of  proteid  food, 
an  omnivorous  animal  may  be  more  tardy  in  manifesting  the 
injurious  action,  which,  however,  is  sure  to  follow  sooner  or 
later  from  any  material  reduction  of  proteid  below  the  cus- 
tomary standards.  In  other  words,  man  as  a  moderate  proteid 
consumer  can  endure  for  a  time  even  large  reductions  in  the 
amount  of  proteid  food,  but  eventually  there  will  be  manifested 
some  of  the  disastrous  results  obtained  with  dogs.  Here,  we 
have  a  somewhat  serious  indictment,  one  that  merits  careful 
consideration.  To  be  sure,  it  may  be  objected  that  between 
dog  and  man  there  is  a  wide  gulf,  and  that  there  is  no  justifi- 
cation for  assuming  that  these  two  types  of  animal  life  have 
anything  in  common.  Still,  the  experience  of  many  years 
has  taught  the  physiologist  that  much  light  can  be  thrown 
upon  the  processes  of  higher  types  of  life  by  a  study  of  what 
occurs  in  lower  forms,  and  on  the  subject  of  nutrition  any 
one  of  experience  would  hesitate  to  cast  out  of  court  the 
evidence  gathered  from  observation  of  what  occurs  among 
the  higher  animals.  It  will  be  the  part  of  wisdom,  therefore, 
to  scrutinize  somewhat  carefully  the  character  of  this  evidence 
obtained  from  a  study  of  the  behavior  of  dogs  toward  a  low 
proteid  diet. 

The  first  series  of  experiments  was  made  in  1891  by  the 
late    Immanuel    Munk    of    Berlin,    privat    docent   of   physi 
ology  at  the  University,  followed  by  further  experiments  in 


EFFECT  OF  LOW  PEOTEID  DIET  233 

1893.1  Four  dogs  in  all  were  studied.  The  diet  made  use  of 
was4'  fleischmehl "  (dried  meat  ground  to  a  powder),  fat  (suet), 
and  rice  boiled  together  with  water.  We  may  refer  briefly  to 
the  details  of  one  experiment.  The  dog  weighed  10.4  kilo- 
grams, and  at  first  was  given  a  daily  diet  composed  of  85 
grams  of  rice,  29  grams  of  fat,  and  30  grams  of  the  flesh 
meal.  This  ration  contained  30.3  grams  of  proteid,  31  grams 
of  fat,  and  66  grams  of  carbohydrate,  with  a  total  fuel  value 
of  663  calories,  or  63  calories  per  kilogram  of  body-weight. 
On  this  diet,  there  was  at  the  outset  a  slight  loss  of  body- 
weight,  after  which  both  body  equilibrium  and  nitrogen  equi- 
brium  were  practically  maintained.  After  this  preliminary 
period  of  three  weeks,  the  day's  diet  was  altered  by  replacing 
15  grams  of  the  proteid  by  15  grams  of  rice,  so  that  the  daily 
ration  consisted  of  15.3  grams  of  proteid  (with  2.42  grams  of 
nitrogen),  31  grams  of  fat,  and  81  grams  of  carbohydrate, 
with  essentially  the  same  fuel  value  per  kilo  of  body-weight 
as  before.  Later,  the  fuel  value  of  the  food  was  further 
increased  by  raising  the  amount  of  rice  to  125  grams  per  day, 
the  day's  ration  then  consisting  of  15.5  grams  of  proteid,  37 
grams  of  fat,  and  96  grams  of  carbohydrate,  with  a  total 
fuel  value  of  780  physiological  heat  units,  or  78  calories 
per  kilo.  On  this  diet,  nitrogen  equilibrium  was  maintained 
and  the  animal  gained  somewhat  in  body-weight.  By  the 
seventh  week,  however,  Munk  reports  that  the  animal  began 
to  show  signs  of  change  ;  there  was  loss  of  appetite,  absorption 
of  the  daily  food  was  impaired,  both  proteid  and  fat  failing  in 
large  degree  to  be  utilized,  while  nitrogen  equilibrium  could 
no  longer  be  maintained.  This  condition  continued  during 
the  next  week,  aggravated  by  vomiting  and  accompanied  by 
loss  of  strength  and  vigor.  At  the  beginning  of  the  tenth 


1  Ueber  die  Folgen  einer  ausreichenden,  aber  eiweissarmen  Nahrung.  Ein 
Beitrag  zur  Lehre  vom  Eiweissbedarf.  Virchow's  Arckiv  fur  pathologische 
Anatomic  und  Physiologic,  Band  132,  p.  91. 


234  THE  NUTRITION  OF  MAN 

week  of  this  low  proteid  ration,  the  animal  was  in  a  very  poor 
condition,  with  complete  loss  of  appetite,  little  inclination  to 
take  food,  etc.  On  feeding  a  liberal  diet  of  fresh  meat,  as 
much  as  250  grains  per  day,  with  some  fat  (50  grams  a  day), 
the  animal  speedily  recovered  its  appetite,  and  in  a  short 
time  was  in  normal  condition,  absorption  of  food  and  utiliza- 
tion of  the  same  being  as  complete  as  at  the  beginning  of  the 
experiment. 

It  is  not  necessary  to  give  further  details  bearing  on  the 
three  additional  experiments.  It  will  suffice  to  quote  the 
general  conclusions  which  Munk  drew  from  the  various  re- 
sults obtained,  viz.,  that  a  low  proteid  intake  in  the  case  of 
dogs  causes  a  loss  of  appetite,  weakness,  vomiting,  etc.,  while 
body- weight  and  nitrogen  equilibrium  are  difficult  or  impos- 
sible to  maintain.  More  specifically,  Munk's  observations  led 
him  to  state  that  for  dogs  of  ten  kilograms  body-weight  a  daily 
intake  of  0.255  gram  of  nitrogen  per  kilo  of  body- weight  is 
not  sufficient  to  maintain  the  normal  condition  of  the  body, 
even  when  the  fuel  value  of  the  day's  food  amounts  to  more 
than  100  calories  per  kilo.  IP  order  to  have  the  animal  con- 
tinue in  nitrogen  and  body  equilibrium,  the  daily  food  must 
contain  at  least  0.31  gram  of  nitrogen  per  kilogram  of  body- 
weight,  with  sufficient  non-nitrogenous  food  to  yield  over 
100  calories  per  kilo. 

Let  us  now  pass  to  the  experiments  made  by  Rosenheim,1 
which  were  carried  on  at  about  the  same  date  as  Munk's.  In 
the  first  experiment,  the  dog  weighed  11.3  kilograms,  and  was 
fed  daily  a  low  proteid  ration  having  a  fuel  value  of  1447 
calories  and  containing  2.825  grams  of  nitrogen.  This  ration 
was  reduced  in  a  short  time  to  a  still  lower  plane,  viz.,  to  1066 


1  Theodor  Rosenheim  :  Ueber  den  Gesundheitsschadigenden  Einflusseiweiss- 
armer  Nahrung.  DuBois-Reymond's  Archiv  fur  Physiologie,  1891,  p.  341. 
Also,  Weiterer  Untersuehungen  iiber  die  Scliadlichkeit  eiweissarmer  Nahrung. 
Pfliiger's  Archiv  f.  d.  gesammte  Physiologic,  Band  54,  p.  61,  1893. 


EFFECT   OF  LOW  PKOTEID  DIET  235 

calories  and  2.525  grams  of  nitrogen  daily.  The  food  as  then 
given  was  composed  of  170  grams  of  rice,  50  grams  of  fat,  and 
25  grams  of  chopped  meat,  on  which  the  dog  gained  weight  and 
preserved  nitrogen  equilibrium.  For  six  weeks,  or  there- 
abouts, the  animal  maintained  its  normal  condition,  after 
which  it  began  to  show  symptoms  of  a  general  disturbance, 
with  lack  of  appetite  and  weakness  accompanied  by  a  condi- 
tion of  icterus.  Addition  of  meat  extract  to  the  diet  to  im- 
prove the  flavor  was  without  any  appreciable  effect.  During 
the  next  two  weeks,  the  condition  of  the  animal  steadily  grew 
worse,  although  the  body-weight  remained  practically  station- 
ary and  nitrogen  equilibrium  was  maintained.  A  week  later, 
the  animal  died  in  a  condition  of  exhaustion,  without  having 
manifested  any  symptoms  of  disturbed  metabolism.  There 
was  found  a  marked  catarrhal  condition  of  the  mucous  mem- 
brane of  the  gastro-intestinal  tract,  with  a  fatty  degeneration 
or  metamorphosis  of  the  glandular  apparatus,  but  nothing  suffi- 
ciently specific  to  account  for  the  peculiar  manner  of  death. 

A  second  experiment  with  a  dog  of  5.8  kilograms,  fed  on 
meat,  fat,  and  rice,  led  to  essentially  the  same  results  as  the 
preceding  experiment.  At  the  end  of  the  first  month,  there 
appeared  indications  that  the  animal  was  not  well,  loss  of  ap- 
petite being  marked,  with  disturbance  of  the  stomach  accom- 
panied by  occasional  vomiting.  These  symptoms  disappeared 
quickly  when  the  animal  was  given  for  a  few  days  large 
quantities  of  meat.  On  returning  to  the  original  low  proteid 
diet,  with  its  large  content  of  rice,  the  symptoms  gradually 
reappeared.  At  the  end  of  two  months  the  animal  had  again 
lost  its  appetite,  and  before  the  end  of  the  fifth  month  the 
subject  was  dead.  Post-mortem  examination  showed  especially 
a  strong  fatty  degeneration  of  the  epithelial  cells  of  the 
mucous  membrane  of  the  stomach  and  intestine.  Rosenheim 
concludes  that  a  diet  poor  in  proteid  is  unhealthful  for  dogs, 
and  that  a  daily  ration  containing  even  0.32  gram  of  nitrogen 


236  THE  NUTRITION   OF  MAN 

per  kilogram  of  body-weight,  and  with  a  fuel  value  of  110 
calories  per  kilo,  is  not  sufficient  to  maintain  the  animal  in  a 
condition  of  health. 

The  next  series  of  experiments  was  made  by  Jagerroos l  of 
Finland.  This  investigator  was  evidently  impressed  by  the 
unfavorable  and  monotonous  character  of  the  diet  made  use 
of  by  the  preceding  investigators,  and  sought  to  introduce  a 
little  variety,  recognizing  also  that  with  a  carnivorous  animal 
it  is  difficult  to  reduce  the  proteid  to  a  low  level  and  maintain 
the  necessary  fuel  value,  without  introducing  foodstuffs  to 
which  the  animal  is  wholly  unaccustomed.  In  the  first  ex- 
periment, the  dog  had  a  body- weight  of  5.77  kilograms,  and 
at  the  beginning  was  fed  daily  40  grams  of  meat  and  100 
grams  of  sugar,  equal  to  0.31  gram  of  nitrogen  and  80  calories 
per  kilo  of  body-weight.  The  experiment  continued  for  eight 
months,  sugar  being  replaced  in  part  by  butter,  and  occasion- 
ally bread,  fat,  and  wheat  meal  being  used  in  proper  amount 
to  yield  the  given  nitrogen  and  fuel  values.  During  the  last 
five  months,  the  intake  of  nitrogen  per  day  averaged  0.29 
gram  per  kilo,  with  a  fuel  value  amounting  to  89  calories 
daily  per  kilo  of  body-weight.  During  this  period,  the  animal 
maintained  a  plus  nitrogen  balance  for  a  large  part  of  the 
time.  The  experiment  was  then  continued  for  two  months 
longer,  with  a  gradual  diminution  in  the  nitrogen  of  the  food 
and  in  the  fuel  value,  the  animal  dying  at  the  end  of  the  tenth 
month. 

In  a  second  experiment,  the  dog  made  use  of  weighed  at 
the  beginning  11.97  kilograms.  During  the  first  five  months, 
the  average  intake  of  nitrogen  amounted  daily  to  0.29  gram 
per  kilo,  while  the  average  fuel  value  of  the  food  (meat,  fat, 
and  sugar)  was  76  calories  per  kilo  daily.  In  the  middle 
of  the  seventh  month  the  animal  was  quite  ill,  with  poor  ap- 

1  B.  H.  Jagerroos  :  Ueber  die  Folgen  einer  ausreichenden,  aber  eiweissarmen 
Nahrung.  Skandinavisches  Archiv  fiir  Physiologic,  Band  13,  p.  376,  1902. 


EFFECT   OF   LOW  PROTEID  DIET  237 

petite,  vomiting,  etc.  Body- weight  began  to  fall  off,  and  the 
animal  soon  died.  With  both  of  these  animals,  the  experi- 
ment ended  suddenly  by  a  sharp  and  short  illness. 

Jagerroos,  however,  believed  that  both  animals  died  from  a 
severe  case  of  infection,  and  not  as  the  result  of  the  diminished 
intake  of  proteid.  This  view  was  fully  substantiated,  in  his 
opinion,  by  the  evidence  furnished  on  bacteriological  and  mor- 
phological examination.  There  was  no  pathological  alteration 
and  no  fatty  degeneration  in  the  intestinal  epithelium  ;  nothing 
to  indicate  any  connection  between  the  lowered  proteid  intake 
and  the  death  of  the  animal.  To  be  sure,  the  long-continued 
diet  poor  in  nitrogen  might  have  diminished  the  power  of  resist- 
ance of  the  body,  but  no  proof  of  this  is  offered.  There  was 
indicated  merely  a  simple  infection,  as  shown  by  the  presence 
of  Streptococcus  and  Bacterium  coli  communis  in  the  blood. 
But,  as  Jagerroos  states,  one  might  well  conceive  of  a  lowered 
power  of  resistance  on  the  part  of  the  body,  due  not  to  any 
change  in  diet,  but  to  the  long-continued  confinement  in  a 
cage  with  the  enforced  inactivity  and  lack  of  freedom.  It  is 
to  be  noted,  furthermore,  that  here  there  was  no  sign  of  a 
gradual  and  progressive  weakening  of  the  body,  no  indication 
of  any  disturbance  of  the  digestive  tract  with  diminished 
power  of  absorption  of  either  fat  or  proteid.  On  the  contrary, 
there  was  a  sudden  and  sharp  attack  of  some  infectious  disease 
by  which  the  animals  quickly  succumbed.  Jagerroos  was  of 
the  opinion  that  in  the  absence  of  this  infection  the  animals 
would  have  continued  to  live  for  a  long  period  of  time. 

If  a  low  proteid  diet  works  so  inimically  on  high  proteid  ani- 
mals as  Munk  and  Rosenheim  thought,  it  would  naturally  be 
expected  that  the  small  proteid  ration  followed  so  long  by 
Jagerroos  would  have  resulted  in  the  appearance  of  marked 
symptoms,  at  least  a  gradual  and  persistent  falling  off  in 
body- weight,  inability  to  maintain  nitrogen  equilibrium,  etc. ; 
but  none  of  these  things  occurred.  In  Munk's  first  experi- 


238  THE  NUTRITION  OF  MAN 

merit,  the  animal  was  given  no  fresh  meat  whatever  during 
four  weeks.  Is  it  not  quite  possible  that  in  the  abrupt  cutting 
off  of  this  wonted  form  of  food  a  disturbance  may  have  been 
set  up  in  the  gastro-intestinal  tract,  which  paved  the  way  for 
the  more  serious  results  that  followed  ?  Jagerroos  uked  only 
fresh,  uncooked  meat  in  his  experiments,  and  laid  great  stress 
upon  the  importance  of  not  departing  any  more  than  was 
necessary  from  the  accustomed  form  of  diet.  The  writer  is 
strongly  of  the  opinion  that  sufficient  stress  has  not  been  laid 
upon  this  phase  of  the  subject.  A  satisfactory  diet  for  dog  as 
for  man  must  meet  ordinary  hygienic  requirements ;  it  must 
not  only  be  sufficient  in  amount,  but  it  must  be  easily  digesti- 
ble, of  accustomed  flavor,  appealing  to  eye,  nostrils,  and  palate, 
with  reasonable  variation  occasionally  and  of  moderate  volume. 
With  due  regard  to  these  conditions,  I  believe  with  Jagerroos 
that  not  much  attention  need  be  paid  to  the  proportion  of 
nitrogen  therein,  for  however  small  the  amount  it  will  be 
found  sufficient  to  meet  the  needs  of  the  body. 

These  are  the  results,  collectively,  so  frequently  used  to 
point  a  moral  for  man :  Beware  of  the  possible  danger  of  re- 
ducing the  consumption  of  proteid  food  below  the  commonly 
accepted  dietary  standards !  We  must  admit,  however,  that 
there  is  a  woeful  lack  of  agreement  in  these  results,  and  it  is 
difficult  to  prevent  a  shadow  of  doubt  from  creeping  over  us 
as  we  try  to  depict  for  ourselves  the  way  in  which  a  low 
proteid  ration  exerts  its  deleterious  effect  on  dogs.  I  do  not 
believe  that  radical  changes  in  diet,  whether  they  involve  in- 
crease or  decrease  in  total  quantities,  or  in  specific  elements 
of  the  diet,  can  be  made  suddenly  without  danger  of  some 
disturbance  of  the  gastro-intestinal  tract  or  other  parts  of  the 
economy,  either  in  dog  or  man.  It  is  reasonable  to  believe 
also  that  a  high  proteid  feeder,  like  a  dog,  with  his  more  lim- 
ited dietary,  will  be  far  more  sensitive  to  great  changes  than 
omnivorous  man  with  his  wider  range  of  foodstuffs.  More- 


EFFECT  OF  LOW  PROTEID  DIET      239 

over,  there  is  just  as  good  ground  for  believing  that  in  any 
animal,  excess  of  proteid  is  as  dangerous  as  a  low  proteid  diet. 
Too  great  a  disturbance  in  the  nutritive  balance,  whether  it 
involves  excess  or  reduction  in  the  amount  of  a  given  food- 
stuff, is  liable  to  be  attended  with  serious  disturbance  in  any 
sensitive  organism. 

In  illustration  of  these  statements,  we  have  some  recent 
results  obtained  by  Watson  and  Hunter 1  upon  the  influence 
of  diet  on  growth  and  nutrition.  These  investigators  find  that 
young  rats  —  two  and  a  half  months  old  —  when  fed  upon  a 
diet  composed  exclusively  of  horse-flesh,  which  is  chiefly  pro- 
teid matter  with  some  fat,  succumb  very  quickly,  for  some 
reason.  Of  fourteen  young  rats  fed  on  this  meat  diet,  six  died 
on  the  third  day.  On  the  morning  of  this  day,  as  the  authors 
state,  "the  rats  appeared  to  be  in  their  usual  health,  but  an  hour 
after  feeding  one  of  them  was  lying  on  its  side  apparently  un- 
conscious. In  a  few  minutes  others  were  affected.  They 
appeared  to  be  paralyzed,  they  felt  cold  to  the  touch,  exhibited 
symptoms  of  tetany,  and  speedily  became  unconscious.  Six 
succumbed  within  half-an-hour.  Of  the  remainder,  some 
showed  similar  symptoms,  although  in  less  degree,  and  they 
recovered  when  the  diet  was  changed  to  bread  and  skim  milk." 
After  two  days  of  the  so-called  normal  diet,  composed  of  bread 
and  skim  milk,  the  remaining  eight  rats  were  again  placed 
on  an  exclusive  meat  diet.  They  appeared  now  to  have 
acquired  a  certain  degree  of  immunity,  for  although  they  ex- 
hibited symptoms  of  deranged  nutrition,  these  were  gradually 
recovered  from  and  they  gained  in  weight.  At  the  end  of  the 
eighth  month,  five  of  the  animals  were  still  alive  and  in  appar- 
ent good  health,  but  their  growth  was  permanently  stunted. 
With  an  exclusive  diet  of  ox-flesh,  young  rats  were  much 


1  Chalmers  Watson,  M.D.,  and  Andrew  Hunter,  M.B. :  Observations  on 
Diet.  The  Influence  of  Diet  on  Growth  and  Nutrition.  Journal  of  Physi- 
ology, Vol.  XXXIV,  p.  112,  1906. 


240  THE  NUTRITION   OF  MAN 

more  liable  to  thrive,  although  their  growth  was  distinctly 
retarded. 

This  difference  in  the  behavior  of  the  animals  towards  the 
two  forms  of  proteid  food  is  to  be  attributed  to  the  fact  that 
ox-flesh  contains  more  fat  than  horse-flesh,  and  consequently 
the  diet  with  this  form  of  meat  was  less  exclusively  proteid 
in  character.  Further,  there  were  some  indications  that  horse- 
flesh is  less  digestible  than  ox-flesh.  Another  fact,  showing 
the  far-reaching  effect  of  a  distinctly  unphysiological  diet,  is 
the  marked  influence  of  pure  meat  food  on  the  progeny. 
Thus,  of  93  rats  born  of  meat-fed  parents  only  19  were  alive 
at  the  end  of  two  months,  while  of  97  young  born  of  bread 
and  milk-fed  rats,  82  were  alive  and  in  apparent  health  at  the 
end  of  the  same  period. 

As  illustrating  how  foods  that  have,  superficially  at  least, 
approximately  the  same  chemical  composition  may  react  dif- 
ferently in  the  animal  body  we  have  the  observations  of  Watson 
on  rats  fed  with  porridge,  made  by  boiling  oatmeal  with  water 
and  skim  milk,  as  contrasted  with  a  diet  of  bread  and  skim 
milk,  the  two  diets  having  essentially  the  same  composition. 
Of  fourteen  young  rats  fed  exclusively  on  porridge,  all,  with 
the  exception  of  two  that  were  withdrawn,  succumbed  within 
five  months,  while  the  bread  and  milk-fed  animals  thrived  as 
usual.  Adult  rats,  however,  can  live  for  prolonged  periods 
and  maintain  their  weight  on  a  porridge  diet.  It  is  believed 
that  the  difference  in  the  behavior  of  young  rats  to  these  two 
closely  allied  forms  of  diet,  is  due  to  a  difference  in  the  diges- 
tibility of  the  food,  the  porridge  being  presumably  less  readily 
digested  by  the  young  animals  than  bread.  With  the  more 
fully  developed  digestive  powers  of  the  adult  animals,  how- 
ever, this  difference  in  availibility  practically  disappears  as  a 
potent  factor  in  their  nutrition.  Finally,  mention  may  be 
made  of  the  fact  that  a  pure  rice  diet,  notably  deficient  in 
proteid,  arrests  the  growth  of  young  rats  and  leads  to  a  fatal 


EFFECT  OF  LOW  PROTEID  DIET  241 

issue  within  three  months,  while  adult  rats  placed  on  such  a 
diet  lose  weight  rapidly  and  die  in  about  the  same  time.  All 
of  these  facts  bearing  on  the  nutrition  of  animals  quite  remote 
from  man  have  significance  as  showing  how  any  wide  departure 
from  a  physiological  diet,  for  that  particular  species  or  type, 
may  lead  to  very  undesirable  results,  and  they  warn  us  not  to 
be  too  hasty  in  drawing  far-reaching  conclusions  and  sweeping 
deductions  from  a  few  experiments  with  a  given  species  of 
animal. 

Recurring  now  to  the  experiments  made  with  dogs,  there 
is  certainly  suggested  an  element  of  danger  in  a  low  proteid 
diet,  which,  if  the  experiments  are  taken  at  their  face  value 
and  the  conclusions  derived  therefrom  applied  to  man,  needs 
careful  consideration.  Jagerroos  plainly  was  not  inclined 
toward  the  belief  that  a  low  nitrogen  intake  was  the  cause 
of  the  unfortunate  results  that  attended  his  experiments. 
Still,  his  animals  did  die  from  some  cause,  and  thereby  his 
position  was  weakened.  Munk  and  Rosenheim,  on  the  other 
hand,  from  their  experiments  were  apparently  convinced  that 
a  low  proteid  intake  was  inimical  to  dogs,  and  it  will  be  re- 
membered Rosenheim  concluded  that  "  a  daily  ration  contain- 
ing even  0.32  gram  of  nitrogen  per  kilogram  of  body- weight, 
and  with  a  fuel  value  of  110  calories  per  kilo,  is  not  sufficient 
to  maintain  the  animal  in  a  condition  of  health."  If  this  is 
really  true,  there  is  some  ground  for  the  arguments  advanced 
by  critical  writers  regarding  the  general  subject  of  nitrogen 
requirements  of  man.  The  evidence  and  the  arguments, 
however,  have  always  seemed  to  the  present  writer  frail  and 
faulty ;  but  recognizing  the  hold  they  have  taken  on  physi- 
ologists and  the  way  they  are  usually  applied  to  man,  I  have 
attempted  to  test  the  matter  experimentally  under  conditions 
which  would  yield  trustworthy  and  conclusive  results. 

The  question  how  far  results  obtained  with  dogs  can  be 
applied  safely  to  man  may  be  open  to  discussion,  but  we  must 

16 


242  THE  NUTRITION   OF  MAN 

first  be  sure  of  our  facts  before  arguments  or  conclusions  of 
any  kind  are  warranted.  It  is  to  be  remembered  that  dogs  are 
as  sensitive  in  many  ways  as  man,  and  no  physiological  ex- 
periment covering  a  long  period  of  time  can  be  carried  out 
with  any  hope  of  success  unless  there  is  due  regard  for  proper 
hygienic  conditions,  some  degree  of  variety  in  diet,  and  rea- 
sonable opportunities  for  fresh  air  and  occasional  exercise.  I 
fancy  that  even  the  most  vigorous  and  hardy  man,  if  confined 
for  six  consecutive  months  in  a  room  just  large  enough  to  fur- 
nish requisite  air-space  and  to  permit  of  extending  his  body  at 
full  length,  would  find  himself  at  the  end  of  such  a  period  in 
a  condition  far  from  healthful,  even  though  there  were  perfect 
freedom  of  choice  in  diet.  If,  however,  there  were  added  to  the 
above  conditions  monotony  in  diet  extending  through  many 
months,  there  would  be  no  occasion  for  surprise  if  the  individ- 
ual lost  appetite  and  strength,  and  showed  signs  of  disturbance 
of  the  gastro-intestinal  tract. 

It  is  doubtful  if  there  is  full  appreciation  of  the  possible 
effect  of  monotony,  in  the  ordinary  dietary  experiments  on 
dogs.  Man  quickly  feels  the  effect ;  the  sportsman  camping 
in  the  woods  by  brook  or  lake  enjoys  his  first  meal  of  speckled 
trout  and  has  no  thought  of  ever  becoming  tired  of  such  a 
delicacy ;  but  as  trout  cooked  in  various  ways  continue  to  be 
placed  before  him  three  times  a  day,  and  with  perhaps  very 
little  else,  he  soon  passes  into  a  frame  of  mind  where  salt 
pork  would  be  a  luxury,  and  where  he  would  prefer  to  go 
hungry  rather  than  eat  the  delicacy,  if  indeed  he  has  appetite 
to  eat  anything.  Is  it  strange  that  dogs  confined  in  cages 
barely  large  enough  to  permit  of  their  turning  around,  and 
fed  day  after  day  and  month  after  month  with  exactly  the 
same  amount  of  desiccated  meat,  fat,  and  rice,  should  show 
signs  and  symptoms,  if  nothing  worse,  of  disturbed  nutrition  ? 
It  is  necessary  in  experiments  of  this  kind  that  the  animals 
be  confined  for  given  periods,  at  least,  since  otherwise  it 


EFFECT   OF  LOW  PHOTEID  DIET  243 

would  be  impossible  to  determine  the  extent  of  nitrogen 
excretion  and  the  rate  of  proteid  katabolism,  etc.  It  is 
possible,  however,  to  limit  the  time  of  close  confinement  to, 
say,  ten  consecutive  days,  this  to  be  followed  by  a  like  period 
of  comparative  freedom,  thus  insuring  opportunities  for  an 
abundance  of  fresh  air  and  exercise. 

The  experiments  of  which  I  wish  to  speak,  and  which  had 
for  their  object  a  study  of  the  effect  of  low  proteid  diet  on 
dogs,  as  types  of  high  proteid  animals,  were  carried  out  at  our 
laboratory  in  the  Sheffield  Scientific  School  and  were  made 
possible  by  liberal  grants  from  the  Carnegie  Institution  of 
Washington,  thus  providing  means  for  securing  the  requisite 
number  of  chemical  assistants.  The  experiments  were  con- 
ducted on  a  somewhat  large  scale,  over  twenty  dogs  being 
made  use  of,  while  many  of  the  experiments  extended  through 
a  full  year.  The  results  in  their  entirety  are  not  yet  ready 
for  publication,  but  I  am  able  to  present  in  a  general  way  ob- 
servations on  six  dogs,  which  will  serve  as  an  ample  illustra- 
tion of  what  may  be  expected  with  high  proteid  animals  when 
living  on  a  low  proteid  diet  under  healthful  conditions.  All 
of  the  six  dogs  whose  cases  are  here  presented  were  fed  on  a 
mixed  diet,  with  some  fresh  meat  each  day ;  bread,  cracker 
dust,  milk,  lard,  and  rice  being  the  other  foods  drawn  upon  to 
complete  the  dietary.  The  animals  were  fed  twice  a  day, 
each  meal  being  accurately  weighed  and  of  definite  chem- 
ical composition.  A  large,  light,  and  airy  room,  kept  scrupu- 
lously clean,  and  in  the  winter  time  properly  heated  by  steam, 
served  as  their  main  abiding  place.  In  this  room  were  a 
suitable  number  of  smaller  compartments,  the  walls  of  which 
were  composed  of  open  lattice  work  (of  iron),  so  as  not  to 
interfere  with  light  or  air,  and  yet  adequate  to  keep  the  dogs 
apart.  These  compartments  were  not  cages  in  the  ordinary 
sense,  but  were  truly  large  and  roomy.  The  entire  floor 
under  the  dogs  was  composed  of  metal,  the  joints  all  soldered, 


244  THE  NUTRITION  OF  MAN 

the  floor  being  sloped  to  a  metal  gutter  in  front  so  that  all 
the  compartments  could  be  flushed  out  each  morning  and 
kept  sweet  and  clean.  In  pleasant  weather,  immediately  after 
their  first  meal,  the  dogs  were  taken  out  of  doors  to  a  large 
enclosure  near  by,  where  they  were  allowed  perfect  freedom 
until  about  four  o'clock,  when  they  were  taken  in  for  their 
second  meal  (between  four  and  five  o'clock  in  the  afternoon). 
The  outdoor  enclosure  was  inaccessible  to  every  one  except 
the  holder  of  the  key,  and  the  dogs  while  there  were  wholly 
free  from  annoyance.  Once  every  month,  during  a  period  of 
ten  consecutive  days,  each  dog  was  confined  in  the  metabolism 
cage  so  as  to  admit  of  the  collection  of  all  excreta,  in  order 
to  make  a  determination  of  the  nitrogen  balance.  Practically, 
therefore,  each  dog  was  in  close  confinement  only  one-third  of 
the  month,  the  remaining  two-thirds  being  spent  in  much  more 
congenial  surroundings.  I  have  entered  thus  fully  into  a  de- 
scription of  the  conditions  prevailing,  because  I  deem  them  ex- 
ceedingly important,  and  because  therein  undoubtedly  lies  the 
explanation  of  the  striking  contrast  between  our  results  and 
those  of  the  earlier  investigators  of  this  subject. 

In  considering  the  outcome  of  our  experiments,  it  may  be 
wise  to  enter  into  some  detail  concerning  the  first  case  to  be 
presented.  The  animal  employed  in  this  experiment  was 
designated  as  No.  5,  and  weighed  on  July  27,  1905,  17.2  kilo- 
grams; it  was  apparently  full  grown,  but  was  thin  and  had 
the  appearance  of  being  underfed.  At  first,  it  was  given  daily 
172  grams  of  meat,  124  grams  of  cracker  dust,  and  72  grams 
of  lard,  the  day's  ration  containing  8.66  grams  of  nitrogen 
and  having  a  fuel  value  of  1389  calories.1  These  figures  are 
equivalent  to  80  calories,  and  0.50  gram  of  nitrogen,  per  kilo- 
gram of  body-weight.  The  animal  took  kindly  to  the  diet, 

1  The  fuel  value  of  the  food  was  calculated  from  the  data  given  in  Bulletin 
No.  28,  U.  S.  Department  of  Agriculture.  All  figures  for  nitrogen  were  ob- 
tained by  exact  chemical  analysis. 


EFFECT   OF  LOW  PKOTEID  DIET 


245 


but  on  August  3  it  refused  to  eat  and  seemed  to  have  a 
little  fever.  The  next  day  it  was  better,  but  for  the  three 
following  days  its  appetite  was  poor,  and  only  a  portion  of 
the  daily  food  was  eaten.  Body- weight  began  to  fall  off,  and 
was  soon  at  15.5  kilograms.  On  the  7th  of  August,  a  dose  of 
vermifuge  was  given,  after  which  the  appetite  returned  and 
the  animal  appeared  in  good  spirits.  From  this  time  forward 
it  seemed  in  perfect  health,  with  good  appetite,  and  showed 
the  usual  vivacity  and  playfulness  of  dog-kind.  The  diet  as 


SUBJECT  No.  5.    DAILY  AVERAGES 


Date. 

Body- 
weight. 

Food. 

Output. 

Nitro- 
gen 
Balance. 
+  or- 

Total 
Nitro- 
gen. 

Nitro- 
gen per 
Kilo 
Body- 
weight. 

Fuel 
Value 
per  Kilo 
Body- 
weight. 

Nitro- 
gen 
through 
Kid- 
neys.1 

Nitro- 
gen 
through 
Excre- 
ment. 

Nitro- 
gen 
through 
Hair. 

1905 
Aug.15-Aug.24 

kilos 
15.8 

grams 

8.66 

gram 
0.54 

calories 

87.3 

grams 
5.44 

gram 

0.70 

gram 
0.52 

grams 

-f-2.00 

Sept.  6-Sept.  15 

17.1 

4.76 

0.27 

72.4 

3.41 

0.32 

0.48 

+0.65 

Oct.  8-Oct  17 

17.6 

4.76 

0.27 

71.8 

3.54 

0.54 

0.49 

+0.19 

Nov.  22-Dec.  1 

16.9 

4.77 

0.28 

72.0 

3.76 

0.39 

0.32 

+0.30 

1906 

Jan.  2-Jan.  11 

17.2 

4.07 

0.23 

72.0 

3.19 

0.54 

0.35 

-0.01 

Jan.  30-Feb.  8 

18.0 

4.07 

0.23 

69.0 

2.87 

0.54 

0.62 

+0.04 

Feb.  27-Mar.  8 

18.2 

5.18 

0.28 

73.0 

3.69 

0.66 

0.74 

+0.09 

Mar.  27-Apr.  5 

18.3 

5.23 

0.28 

73.0 

3.66 

0.84 

0.48 

+0.25 

Apr.  24-May  3 

19.1 

6.22 

0.27 

68.0 

3.76 

0.38 

0.48 

+0.60 

May  22-May  31 

19.4 

5.22 

0.26 

65.0 

3.44 

0.31 

0.48 

+0.99 

June  17-June  26 

20.0 

5.24 

0.26 

67.0 

3.50 

0.71 

0.48 

+0.55 

specified  was  continued  unchanged  until  August  25,  a  balance 
experiment  covering  a  period  of  ten  days,  from  the  15th  to 

1  All  through  the  balance  periods  the  dogs  were  catheterized  each  morn- 
ing to  insure  complete  collection  of  the  twenty-four  hours'  urine. 


246  THE  NUTRITION  OF  MAN 

the  24th  of  August  inclusive,  being  carried  out,  in  which  the 
nitrogen  of  the  intake  was  compared  with  the  output  for  each 
day.  From  the  accompanying  table,  where  are  given  the 
average  values  of  all  the  balance  periods  of  the  experiment, 
it  is  to  be  seen  that  during  this  first  period  the  animal  was 
laying  on  or  gaining  an  average  of  2  grams  of  nitrogen  per 
day. 

On  August  25,  a  radical  change  was  made  in  the  diet, 
by  reducing  the  amount  of  meat  to  70  grams  daily,  thereby 
lowering  the  intake  of  nitrogen  to  4.76  grams,  or  0.27  gram 
per  kilo  of  body-weight ;  the  cracker  dust  and  lard  being  kept 
at  essentially  the  same  levels  as  before.  This  diet  was  con- 
tinued through  the  next  balance  period,  the  dog  in  the  mean- 
time gaining  in  body-weight,  and  showing  for  the  second 
balance  period  an  average  gain  by  the  body  of  half  a  gram  of 
nitrogen  per  day.  The  food  was  then  altered  by  substituting 
bread  for  the  cracker  dust,  but  so  adjusted  that  the  nitrogen 
and  fuel  values  of  the  day's  food  remained  practically  un- 
changed. There  was  still,  however,  a  gain  in  body-weight 
and  a  slight  gain  in  body  nitrogen.  At  the  close  of  the  third 
balance  period,  the  diet  was  again  altered,  one-half  of  the 
meat  being  replaced  by  milk,  while  cracker  dust  was  substi- 
tuted for  the  bread.  The  morning  meal  consisted  of  170 
grams  of  milk,  86  grams  of  cracker  dust,  and  18  grams  of 
lard,  while  the  afternoon  meal  was  composed  of  35  grams  of 
meat,  63  grams  of  cracker,  and  35  grams  of  lard.  The  day's 
ration,  however,  still  contained  4.76  grams  of  nitrogen  and 
had  a  fuel  value  of  1249  calories.  This  diet  was  maintained 
until  November  20,  when  the  animal  was  again  placed  on  a 
daily  ration  of  meat  (69  grams),  bread  (166)  grams,  and 
lard  (80  grams),  with  a  total  fuel  value  of  1228  calories  and 
4.77  grams  of  nitrogen.  This  was  continued  until  December 
2,  the  dog  still  showing  a  plus  nitrogen  balance,  but  with  a 
little  loss  in  body- weight.  On  December  2f  the  diet  was  again 


August   19,  1905 


Subject  No.     5.  Xoi'ciiihcr   18, 


Subject  No.    5.  April  24,  1906 


Subject  No.    5.  June  27,  1906 


EFFECT   OF  LOW  PEOTEID  DIET  247 

changed  by  substituting  milk  for  a  portion  of  the  meat,  but 
the  nitrogen  and  fuel  values  were  maintained  at  the  same 
level  as  before.  After  a  week,  December  9,  the  food  was 
modified  as  follows :  the  morning  meal  contained  170  grams 
of  milk,  110  grams  of  rice,  amd  11  grams  of  lard,  while  the 
afternoon  meal  was  composed  of  35  grams  of  meat,  81  grams 
of  rice,  and  30  grams  of  lard.  The  total  nitrogen  content 
of  the  day's  ration  was  4.07  grams,  while  the  fuel  value  was 
1255  calories.  At  this  time,  the  animal  weighed  17.1  kilo- 
grams, consequently  the  intake  of  nitrogen  had  been  re- 
duced to  0.23  gram  per  kilo  of  body- weight,  while  the  fuel 
value  stood  at  73  calories  per  kilogram.  This  diet  was  con- 
tinued until  February  9,  the  balance  period,  between  January  2 
and  11,  showing  that  the  animal  was  in  nitrogen  equilibrium, 
in  spite  of  the  material  reduction  in  the  intake  of  proteid,  and 
that  body-weight  was  increasing.  The  next  balance  period, 
January  30  to  February  8,  showed  still  further  gain  in  weight 
with  continuance  of  nitrogen  equilibrium.  On  February  9,  the 
diet  was  changed  by  returning  to  70  grams  of  meat,  158  grams 
of  cracker  dust,  and  60  grams  of  lard,  with  a  daily  intake  of 
0.28  gram  of  nitrogen  per  kilo  of  body- weight. 

In  this  manner,  the  experiment  was  continued  with  frequent 
changes  in  the  character  of  the  diet,  but  always  maintaining 
essentially  the  same  values  in  nitrogen  and  calories  as  shown 
in  the  table,  until  June  27 ;  having  extended  through  just  eleven 
months,  with  the  animal  at  the  close  of  the  experiment  still 
gaining  in  body-weight,  with  a  steady  plus  balance  of  nitro- 
gen, and  with  every  indication  of  good  health  and  strength. 
For  ten  months  the  animal  lived  with  perfect  comfort  and  in 
good  condition  on  an  average  daily  intake  of  0.26  gram  of 
nitrogen  per  kilogram  of  body-weight,  and  with  an  average 
fuel  value  of  70.3  calories  per  kilo.  Further,-  it  is  to  be  ob- 
served that  at  no  time  during  the  ten  months  did  the  daily  in- 
take of  nitrogen  rise  above  0,28  gram  per  kilo,  while  during  one 


248  THE  NUTRITION   OF  MAN 

month  it  fell  to  0.23  gram  per  kilo.  Similarly,  the  fuel  value 
of  the  daily  food  never  exceeded  73  calories  per  kilo,  while  at 
times  it  dropped  as  low  as  67  and  65  calories  per  kilo.  That 
this  diet  was  more  than  sufficient,  both  in  nitrogen  and  fuel 
value,  is  indicated  by  the  steady  increase  in  body -weight  and 
by  the  plus  nitrogen  balances  observed  in  most  of  the  periods 
throughout  the  experiment.  Indeed,  with  the  comparatively 
low  degree  of  muscular  activity  which  this  animal  was  accus- 
tomed to,  it  would  have  been  unwise  to  have  kept  the  subject 
much  longer  on  a  diet  so  rich  as  the  above,  since  there  would 
have  been  danger  of  detriment  to  its  health  and  good  condi- 
tion. When  these  results  are  contrasted  with  the  statements 
of  Munk  and  Rosenheim,  the  latter  of  whom  found  that  even 
0.32  gram  of  nitrogen  and  110  calories  per  kilo  were  insufficient 
to  maintain  dogs  in  a  condition  of  health,  it  is  plain  that  for 
some  reason  our  results  are  quite  at  variance  with  their 
findings. 

The  accompanying  photographs,  taken  on  August  19,  1905, 
February  27,  April  24,  and  at  the  close  of  the  experiment  on 
June  27,  1906,  show  the  appearance  of  the  animal  at  the 
respective  dates,  and  indicate  more  clearly  than  words  can 
express  the  actual  condition  of  the  animal. 

Turning  now  to  a  second  subject,  designated  as  dog  No.  3, 
the  experiment  with  which  lasted  for  nearly  an  entire  year, 
the  following  general  statements  may  be  made.  The  animal 
was  a  small  black  and  white  fox  terrier,  weighing  on  July  6, 
1905,  6.5  kilograms.  It  was  a  nervous,  affectionate  little 
creature,  far  less  phlegmatic  than  the  animal  just  described, 
always  on  the  alert  for  a  petting,  and  unceasingly  active.  For 
these  reasons,  it  seemingly  required  per  kilogram  of  body- 
weight  a  little  more  food  than  the  preceding  animal;  a  fact 
also  in  harmony  with  the  general  law  that  small  animals,  per 
unit  of  body-weight,  need  more  food  than  larger  ones.  The 
diet  made  use  of  was  of  the  same  general  character  as  em- 


Sitl'jcct  No.    3.  August   19,  1905 


Subject  No.     j.  November   18,   1905 


Subject  No.    3.  April  24,  1906 


r  ^ 


F 


Subject  No.    3.  June   27,    1906 


EFFECT  OF  LOW  PROTEID  DIET 


249 


ployed  with  the  preceding  animal,  and  was  changed  from  time 
to  time  to  give  requisite  variety  and  to  insure  freedom  from 
too  great  monotony.  The  accompanying  table,  showing  daily 
averages  during  the  twelve  balance  periods,  gives  all  necessary 
information  regarding  the  outcome  of  the  experiment. 

SUBJECT  No.  3.    DAILY  AVERAGES 


Date. 

Body- 
weight. 

Food. 

Output. 

Nitro- 
gen 
Balance 
+  or  — 

Total 
Nitro- 
gen. 

Nitro- 
gen per 
Kilo 
Body- 
weight. 

Fuel 
Value 
per  Kilo 
Body- 
weight. 

Nitro- 
gen 
through 
Kid- 
neys. 

Nitro- 
gen 
through 
Excre- 
ment. 

Nitro- 
gen 
through 
Hair. 

1905 
July  IB-July  28 

kilos 
6.8 

grams 
5.88 

gram 
0.84 

calories 

79.0 

grams 
5.58 

gram 

0.43 

gram 
0.05 

gram 

-0.18 

Aug.15-Aug.24 

7.1 

3.44 

0.49 

77.4 

3.35 

0.17 

0.13 

-0.21 

Sept.  6-Sept.  16 

6.9 

2.11 

0.30 

80.0 

1.93 

0.21 

0.07 

-0.10 

Oct.  8-Oct.  17 

6.9 

2.10 

0.30 

80.0 

1.83 

0.20 

0.07 

0 

Nov.  22-Dec.  1 

6.0 

1.83 

0.31 

80.0 

1.48 

0.21 

0.11 

+0.03 

1906 
Jan.  2-Jan.  11 

5.6 

1.63 

0.29 

81.0 

1.54 

0.17 

0.08 

-0.16 

Jan.  30-Feb.  8 

5.5 

1.63 

0.30 

82.0 

1.60 

0.15 

0.06 

-0.17 

Feb.  27-Mar.  8 

5.5 

1.78 

0.32 

84.0 

1.66 

0.17 

0.05 

-0.10 

Mar.  27-Apr.  5 

5.7 

1.98 

0.34 

81.0 

1.75 

0.21 

0.06 

-0.04 

Apr.  24-May  3 

5.7 

1.98 

0.34 

83.0 

1.68 

0.13 

0.13 

+0.04 

May  22-May  31 

6.8 

1.98 

0.34 

80.0 

1.77 

0.13 

0.11 

-0.03 

June  17-June  26 

6.0 

1.98 

0.33 

77.0 

1.53 

0.21 

0.07 

+0.17 

It  will  be  observed  that  during  the  first  three  months  the 
animal  showed  a  tendency  to  gain  in  weight  slightly,  recalling 
that  its  initial  weight  on  July  6  was  6.5  kilograms.  Later, 
the  weight  fell  off  a  little,  but  in  March  it  showed  an  upward 
movement,  though  very  gradual.  With  the  amount  of  proteid 
food  given,  it  is  evident  that  the  animal  needed  about  80 
calories  per  kilo  to  maintain  a  condition  of  body-equilibrium. 


250 


THE  NUTEITIOK  OF  MAN 


Nitrogen  equilibrium  was  practically  maintained  throughout 
the  larger  portion  of  the  twelve  months,  but  evidently  the 
animal  required  0.31-0.33  gram  of  nitrogen  per  kilogram  of 
body-weight.  Attention  may  be  directed,  in  view  of  the  re- 
sults reported  by  Munk  regarding  loss  of  the  power  of  absorp- 
tion and  utilization  of  proteid  food,  to  the  figures  showing 
the  average  daily  output  of  nitrogen  through  the  excrement. 
It  is  plain  from  the  data  presented,  that  this  animal  was  not 
suffering  from  any  trouble  of  this  order  ;  indeed,  the  utiliza- 
tion of  proteid  food  throughout  the  entire  experiment  was 
exceedingly  complete,  as  shown  by  the  relatively  small  loss  of 
nitrogen  through  the  excrement,  thus  implying  vigorous  and 


SUBJECT  No.  13.    DAILY  AVERAGES 


Date. 

Body- 
weight. 

Food. 

Output. 

Nitro- 
gen 
Balance 
-for- 

Total 
Nitro- 
gen. 

Nitro- 
gen per 
Kilo 
Body- 
weight. 

Fuel 
Value 
per  Kilo 
Body- 
weight. 

Nitro- 
gen 
through 
Kid- 
neys. 

Nitro- 
gen 
through 
Excre- 
ment. 

Nitro- 
gen 
through 
Hair. 

1905 
Sept.  24-Oct.  3 

kilos 

14.0 

grams 
7.22 

gram 
0.52 

calories 
86.0 

grams 
6.40 

gram 

0.71 

gram 

0.19 

gram 
-0.08 

Nov.  5-Nov.  14 

13.0 

4.78 

0.35 

80.0 

4.29 

0.37 

0.25 

-0.13 

Dec.  19-Dec.  28 

13.4 

3.70 

0.27 

72.0 

2.86 

0.49 

0.13 

+0.22 

1906 
Jan.  16-Jan.  25 

14.1 

3.72 

0.26 

70.0 

3.16 

0.61 

0.16 

-0.21 

Feb.  13-Feb.  22 

14.3 

4.26 

0.30 

78.0 

3.54 

0.67 

0.37 

-0.32 

Mar.  13-Mar.  22 

14.1 

3.62 

0.26 

65.0 

3.29 

0.46 

0.14 

-0.27 

Apr.  10-Apr.  19 

14.2 

4.59 

0.32 

73.0 

2.84 

0.51 

0.10 

+1.14 

May  8-May  17 

14.2 

4.59 

0.32 

71.0 

3.56 

0.48 

0.18 

+0.37 

June  5-June  14 

15.3 

4.58 

0.30 

66.0 

2.98 

0.55 

0.28 

+0.77 

unimpaired  digestion,  together  with  thorough  absorption  of 
the  products  formed. 

The  accompanying  photographs  show  the  appearance  of  the 


Subject  No.  13.  January  2,  1906 


Subject  No.  13.  February  27,  1906 


Subject  No.  13.  April  24,  1906 


'ubjcct  No.  /j.  June   ig,    1906 


EFFECT   OF   LOW  PEOTEID  DIET 


251 


animal  on  August  19,  1905,  November  18,  1905,  April  3  and 
June  27,  1906,  the  close  of  the  experiment. 

Passing  now  to  the  third  subject,  we  have  an  experiment  of 
somewhat  shorter  duration,  viz.,  of  nine  months,  but  suf- 
ficiently long  to  afford  ample  opportunity  for  any  deleterious 

SUBJECT  No.  15.    DAILY  AVERAGES 


Date. 

Body- 
weight. 

Food. 

Output. 

Nitro- 
gen 
Balance 
+  or- 

Total 
Nitro- 
gen. 

Nitro- 

Body- 
weight. 

Fuel 
Value 
per  Kilo 
Body- 
weight. 

Nitro- 
gen 
through 
Kid- 
neys. 

Nitro- 
gen 
through 
Excre- 
ment. 

Nitro- 
gen 
through 
Hair. 

1905 
Nov.  5-Nov.  14 

kilos 
9.2 

grams 

3.35 

gram 
0.36 

calories 

82.0 

grams 

2.95 

gram 

0.11 

gram 

0.14 

gram 

+0.15 

Dec.  19-Dec.  28 

8.9 

2.61 

0.30 

75.0 

2.47 

0.12 

0.12 

-0.10 

1906 

Jan.  16-Jan.  25 

8.7 

2.60 

0.30 

79.9 

2.15 

0.21 

0.16 

+0.08 

Feb.  13-Feb.  16 

8.5 

2.61 

0.30 

82.0 

2.37 

0.20 

0.15 

-0.11 

Mar.  13-Mar.  22 

8.7 

2.82 

0.32 

80.0 

2.68 

0.17 

0.19 

-0.22 

Apr.  10-Apr.  19 

9.0 

2.80 

0.31 

82.0 

2.14 

0.26 

0.09 

+0.31 

May  8-May  17 

9.5 

2.83 

0.30 

75.0 

2.26 

0.30 

0.12 

+0.15 

June  5-  June  14 

10.2 

2.81 

0.27 

70.0 

2.26 

0.28 

0.24 

+0.03 

effect  to  manifest  itself.  The  initial  weight  of  the  dog, 
No.  13,  was  14.5  kilograms  on  September  14.  The  lowest 
intake  of  nitrogen  was  0.26  gram  per  kilo  of  body-weight  per 
day,  while  the  fuel  value  of  the  daily  food  was  during  one 
period  reduced  to  55  calories  per  kilo.  A  daily  proteid  con- 
sumption equalling  0.30  gram  of  nitrogen  per  kilo,  with  a 
total  fuel  value  in  the  day's  food  of  66-70  calories  per  kilo,  was 
clearly  quite  sufficient  to  maintain  nitrogen  equilibrium  and 
body-weight ;  indeed,  toward  the  end  of  the  experiment,  the 
animal  commenced  to  gain  in  weight  quite  noticeably  on  the 
above  diet,  and  was  laying  by  fairly  large  amounts  of  nitro- 


252 


THE  NUTRITION   OF  MAN 


gen  daily.  The  accompanying  table  gives  the  average  daily 
nitrogen  exchange,  etc.,  of  the  nine  balance  periods,  while  the 
photographs,  taken  on  the  dates  indicated  under  each,  show 
the  appearance  of  the  animal  at  various  times. 

Results  of  the  same  general  tenor  with  dogs  No.  15  and 
No.  20  are  seen  in  the  appended  tables,  while  the  ac- 
companying photographs  testify  clearly  to  the  general  good 
condition  of  the  animals  up  to  the  end  of  the  experiments. 
In  No.  20  particularly,  the  great  gain  in  body- weight  is 
to  be  noted,  even  though  the  fuel  value  of  the  food  was 
reduced  as  low  as  64  calories  per  kilo,  with  the  nitrogen  intake 
at  0.28  gram*  per  kilo  daily.  Plainly,  the  day's  food  could 
have  been  diminished  still  more,  with  perfect  safety  to  both 
body  and  nitrogen  equilibrium. 


SUBJECT  No.  20.    DAILY  AVERAGES 


Food. 

Output. 

TSTifrn 

Date. 

Body- 
weight. 

Total 
Nitro- 
gen. 

Nitro- 

"ST 

Body- 

Fuel 
Value 
per  Kilo 
Body- 

Nitro- 
gen 
through 
Kid- 

Nitro- 
gen 
through 
Excre- 

Nitro- 
gen 
through 

Tpr_  • 

-W  1  trO- 

gen 
Balance 
+  or- 

weight. 

weight. 

neys. 

ment. 

.ti  air. 

1905 

kilos 

grams 

gram 

calories 

grams 

gram 

gram 

gram 

Dec.  6-Dec.  15 

15.9 

8.35 

0.52 

82.0 

6.03 

0.74 

0.38 

+1.20 

1906 

Jan.  16-Jan.  25 

16.4 

4.47 

0.27 

73.0 

3.61 

0.65 

0.15 

+0.16 

Feb.  13-Feb.  22 

17.2 

4.45 

0.25 

72.0 

3.92 

0.36 

0.13 

+0.04 

Mar.  13-Mar.  22 

17.4 

5.00 

0.28 

72.0 

6.49 

0.33 

0.10 

-0.92 

Apr.  10-Apr.  19 

18.4 

5.60 

0.30 

69.0 

4.88 

0.62 

0.18 

+0.02 

May  8-May  17 

19.6 

6.58 

0.28 

69.0 

3.86 

0.75 

0.38 

+0.60 

June  6-June  14 

19.7 

5.59 

0.28 

64.0 

4.69 

0.45 

0.40 

+0.05 

The  illustrations  so  far  presented,  with  the  general  agree- 
ment in  the  character  of  the  results,  might  perhaps  be  inter- 
preted as  indicating  that  there  is  no  difficulty  whatever  in 


Subject  No.   75.  January  2,  1906 


Subject  No.  75.  February  27,  7906 


Subject  No.  15.  April  24,  1906 


Subject  No.  ij.  June  19,  1906 


EFFECT   OF  LOW  PROTEID  DIET  253 

bringing  a  high  proteid  consumer,  like  a  dog,  down  to  a  low 
level  of  proteid  consumption.      This,  however,  would  be  a 
false  impression.     Much  depends  upon  the  character  of  the 
proteid  food,  at  least  where  any  attempt  at  rapid  change  is 
made,  for  a  certain  modicum  of  meat  or  other  animal  food 
seems  a  necessary  part  of  the  daily  diet  if  health  and  strength 
are  to  be  maintained.     A  dog  transferred  suddenly  from  a 
daily  ration  in  which  meat  and  milk  are  conspicuous  elements 
to  a  diet  in  which  these  are  wholly  wanting  is  very  liable  to 
show  disturbing  symptoms  almost   immediately.     One  case 
may  be  cited  in  illustration  of  these  statements.     On  Septem- 
ber 29, 1905,  dog  No.  17,  weighing  18.2  kilos,  was  placed  on 
a  daily  diet  composed  of  70  grams  of  fresh  meat,  442  grams 
of  milk,  300  grams  of  bread,  and  28   grams  of  lard.      This 
ration  contained  9.06  grams  of  nitrogen  and  had  a  fuel  value 
of  1465  calories,  or  0.5  gram  of  nitrogen  and  80  calories  per 
kilogram  of  body-weight.    On  October  11,  the  animal  weighed 
18.6  kilograms  and  was  in  perfect  condition.    On  the  13th,  the 
meat  was  reduced  to  34  grams  per  day,  but  the  milk  was  in- 
creased in  amount  so  as  to  maintain  the  same  nitrogen  intake 
and  fuel  value  as  before.      This  diet  was  continued  until  No- 
vember 3,  a  balance  experiment  covering  ten  days  from  October 
22  to  the  31  inclusive,  showing  that  the  animal  was  laying 
by  a  little  nitrogen.     On  November  3,  the  diet  was  changed  to 
milk,  bread,  and  lard,  the  fuel  value  being  maintained  at  80 
calories  per  kilo  daily,  while  the  nitrogen  intake  was  reduced 
to  0.30  gram  per  kilo.     On  this  diet,  the  animal  seemed  to 
thrive    perfectly,    and   at   the   end  of  two  weeks  showed    a 
body-weight  of   18.2   kilograms.       November  19,    the   milk 
was  withdrawn,  the  bread  being  increased  so  as  to  keep  the 
daily  nitrogen  intake  and  the  fuel  value  unchanged.     The 
day's  food  was  now  composed  of  bread  and  lard  solely,  but,  as 
just  stated,  the  nitrogen  and  fuel  values  were  unaltered.      In 
four  days'  time,  however,  a  change  began  to  creep  over  the 


254  THE  NUTRITION  OF  MAN 

animal;  the  appetite  diminished,  and  there  was  apparent  a 
condition  of  lassitude  and  general  weakness  which  deterred 
the  animal  from  moving  about  as  usual. 

During  the  next  week  the  animal  grew  steadily  worse,  and 
would  eat  only  when  coaxed  with  a  little  milk  or  with  bread 
softened  with  milk,  the  diet  of  bread  and  lard  being  invari- 
ably refused.  There  was  marked  disturbance  of  the  gastro- 
intestinal tract ;  bloody  discharges  were  frequent ;  the  mucous 
membrane  of  the  mouth  was  greatly  inflamed  and  very  sore ; 
body- weight  fell  off,  and  the  animal  was  in  a  very  enfeebled 
condition.  This  continued  until  December  4,  with  every  in- 
dication that  the  animal  would  not  long  survive,  but  by 
feeding  carefully  with  a  little  milk  and  occasionally  some 
meat,  improvement  finally  manifested  itself,  and  by  December 
18  there  was  good  appetite,  provided  bread  was  not  conspicu- 
ous in  the  food.  Body-weight,  which  had  fallen  to  15.5  kilos, 
was  being  slowly  regained,  and  on  December  30  the  animal 
was  again  placed  on  a  weighed  diet,  consisting  of  70  grams  of 
meat,  442  grams  of  milk,  210  grams  of  cracker  dust,  and  10 
grams  of  lard.  This  diet  contained  8.26  grams  of  nitrogen 
and  had  a  fuel  value  of  1330  calories,  equivalent  to  0.5  gram 
nitrogen  and  80  calories  per  kilogram  of  body-weight.  On 
January  12, 1906,  the  weight  of  the  animal  was  16.7  kilos, 
while  in  general  condition  there  was  nothing  to  be  desired. 
The  food  was  then  modified  by  diminishing  the  amounts  of 
meat  and  milk  fed  daily  by  one-half,  thus  reducing  the  nitrogen 
intake  to  0.35  gram  per  kilo  of  body-weight,  but  maintaining 
the  fuel  value  of  the  food  at  80  calories  per  kilo.  Under  this 
regime,  body-weight  still  increased,  and  on  January  27  was 
17.5  kilograms.  A  balance  period,  shown  in  the  accompany- 
ing table,  extending  from  January  30  to  February  8,  affords 
ample  evidence  that  the  body  was  laying  by  nitrogen. 


Subject  No.  20.  January  2,  1006 


Subject  No.  20.  February  27,  1006 


Subject  No.  20.  April  24,  ioc6 


Subject  No.  20.  June  ig,  1006 


EFFECT   OF  LOW  PKOTEID  DIET 


255 


SUBJECT  No.  17.    DAILY  AVERAGES 


Date. 

Body- 
weight. 

Food. 

Output. 

Nitro- 

Balance 
-j-or- 

Total 
Nitro- 
gen. 

Nitro- 
gen 
per  Kilo 
Body- 
weight. 

Fuel 
Value 
per  Kilo 
Body- 
weight. 

Nitro- 
gen 
through 
Kid- 
neys. 

Nitro- 
gen 
through 
Excre- 
ment. 

Nitro- 
gen 
through 
Hair. 

1905 

Oct.  22-Oct.  31 

kilos 
18.3 

grams 

9.06 

gram 
0.49 

calories 
80.0 

grams 

7.73 

gram 

0.66 

gram 

0.28 

gram 
+0.39 

1906 

Jan.  30-Feb.  8 

17.6 

5.77 

0.33 

78.0 

4.12 

0.44 

0.21 

+1.00 

Feb.  27-Mar.  8 

17.9 

5.31 

0.30 

72.0 

4.59 

0.59 

0.37 

-0.24 

Mar.  27-Apr.  5 

18.1 

5.33 

0.29 

70.0 

5.63 

0.89 

0.27 

-1.52 

Apr.  24-May  3 

18.4 

5.90 

0.32 

68.0 

5.06 

0.49 

0.30 

+0.05 

May  22-May  31 

18.6 

5.90 

0.31 

67.0 

5.25 

0.53 

0.43 

-0.31 

June  17-June  26 

19.9 

5.89 

0.29 

70.0 

4.29 

0.39 

0.28 

+0.93 

In  all  of  the  subsequent  months,  a  small  amount  of  meat 
was  a  part  of  the  daily  food,  but  as  is  seen  from  the  table  of 
balance  periods,  the  total  nitrogen  intake  and  the  fuel  value 
of  the  food  were  reduced  to  even  lower  levels  per  kilogram  of 
body-weight.  Yet  the  animal  gained  steadily,  until  at  the 
latter  part  of  June  the  weight  was  considerably  above  that 
noted  at  the  commencement  of  the  experiment  in  the  preced- 
ing October.  Further,  the  animal  was  in  nitrogen  equilibrium 
or  even  gaining  nitrogen,  and  in  perfect  condition  of  health 
and  vigor,  as  is  indicated  by  the  accompanying  photographs 
taken  at  the  different  periods  stated.  Especially  to  be  em- 
phasized is  the  fact  that  during  the  last  six  months  of  the 
experiment,  the  daily  intake  of  nitrogen  and  the  fuel  value  of 
the  food  were  as  low  or  even  lower  than  in  November,  when 
the  daily  diet  was  limited  to  bread  and  lard.  The  disastrous 
result  which  showed  itself  at  once  on  this  latter  diet,  with  all 
animal  food  excluded,  was  not  due  to  low  proteid  or  to  defi- 
ciency in  fuel  value,  but  simply  to  the  fact  that  the  animal  for 


256  THE  NUTRITION  OF  MAN 

some  reason  could  not  adjust  itself  to  a  simple  dietary  of 
bread  and  fat,  although  there  was  ample  available  nitrogen  and 
fuel  value  for  the  body's  needs.  Something  was  lacking, 
which  meat  or  milk  could  supply,  and  this  something  was 
indispensable  for  the  maintenance  of  the  normal  nutritional 
rhythm. 

This  is  by  no  means  an  exceptional  case,  but  we  can  cite 
many  other  examples  of  like  results  where  the  animal  when 
restricted  to  a  purely  vegetable  diet,  such  as  bread,  pea-soup, 
bean  soup,  etc.,  reinforced  by  an  animal  fat,  quickly  passed 
from  a  condition  of  health  into  a  state  of  utter  wretchedness, 
with  serious  gastro-intestinal  disturbance.  The  results  are 
not  to  be  attributed  to  the  lower  utilization  of  the  vegetable 
food,  for  the  disastrous  effect  is  too  quickly  manifest,  and 
further,  often  shows  itself  when  the  animal  plainly  has  a 
large  store  of  available  nutriment  in  its  own  tissues. 

This  experiment  with  dog  No.  17  has  been  dwelt  upon  at 
some  length,  because  it  illustrates  a  very  important  principle 
in  the  nutrition  of  a  high  proteid  and  carnivorous  animal.  As 
before  stated,  it  is  not  a  question  of  high  or  low  proteid  simply, 
but  involves  possibly  the  more  subtle  question  of  the  relative 
value  of  specific  forms  of  proteid  food.  It  will  be  noted  that 
this  statement  is  made  somewhat  guardedly,  in  harmony  with 
the  caution  necessarily  called  for  in  view  of  our  lack  of 
knowledge  regarding  the  possible  need  of  the  animal's  body 
for  extraneous  principles  which  only  meat,  milk,  or  other 
animal  products  can  supply.  Inorganic  salts,  nitrogenous 
extractives,  and  other  substances  without  any  appreciable  fuel 
value,  are  quite  likely  to  be  of  primary  importance  in  control- 
ling and  regulating  the  various  processes  of  the  body,  which 
combine  to  maintain  the  condition  of  normal  nutrition.  With 
a  diet  restricted  to  one  or  two  vegetable  products,  it  is  quite 
conceivable  that  something  may  be  lacking  which  the  system 
demands,  though  it  cannot  be  measured  in  terms  of  nitrogen 


Subject  No.  17.  January  2,  ipo<5 


Subject  No.  17.  February  27,  /pod 


Subject  No.  17.  April  24,  1906 


Subject  No.  77.  June  27,  1906 


EFFECT   OF  LOW  PKOTEID  DIET  257 

or  calories.  It  may  be  said  that  man  thrives  on  a  purely 
vegetable  diet,  but  while  this  is  unquestionably  true,  it  must 
be  remembered  that  man  with  his  free  choice  of  food  has  re- 
course, as  a  rule,  to  a  large  variety  of  vegetable  products  from 
many  sources,  and  consequently  there  is  great  likelihood  of 
his  absorbing  from  these  varied  products  such  supplementary 
matters  as  may  be  needed.  On  this  question,  we  are  in  a 
realm  of  doubt  and  uncertainty,  but  the  possibilities  suggested 
must  not  be  ignored,  for  they  may  contain  a  germ  of  truth  of 
the  utmost  importance.  The  fact  remains,  however,  that  a 
dog  when  restricted  to  a  purely  vegetable  dietary  does  not 
thrive ;  a  little  animal  food  seems  necessary  to  keep  up  health 
and  strength,  and  this  suffices  even  though  the  daily  nitrogen 
intake  and  fuel  value  of  the  food  are  restricted  to  a  level  be- 
low that  of  the  vegetable  dietary. 

With  these  facts  before  us,  it  is  difficult  to  avoid  the  con- 
clusion that  some  significance  may  attach  to  the  specific  nature 
of  the  proteid.  Of  course,  we  must  not  overlook  the  radical 
difference  in  dietary  habits  of  man  and  dog.  Man  as  an  om- 
nivorous creature  has  for  generations  been  accustomed  to  par- 
take largely  of  vegetable  foods,  and  as  a  result  his  digestive 
tract  and  his  system  as  a  whole  has  become  acclimated,  as  it 
were,  to  the  nutritive  effects  of  vegetable  matter.  Dogs,  011 
the  other  hand,  are  typical  carnivores,  and  their  habits  for 
generations  have  led  in  an  opposite  direction,  so  that  their 
gastro-intestinal  tracts  and  their  systems  have  become  accus- 
stomed  to  the  effects  of  a  diet  in  which  animal  food  largely 
predominates.  Whether  these  deeply  ingrained  characteristics 
are  responsible  in  any  large  measure  for  the  difference  in 
behavior  of  man,  on  a  purely  vegetable  diet,  and  dogs  is  open 
to  question.  It  would  certainly  not  be  strange  if  such  were 
the  case,  but  as  we  look  at  the  facts  collected  in  our  study  of 
this  subject,  it  is  somewhat  impressive  to  note  how  well  dogs 
thrive  on  a  relatively  large  amount  of  vegetable  food,  pro- 

17 


258  THE  NUTRITION   OF  MAN 

vided  there  is  a  modicum  of  animal  food  added  thereto.  In 
other  words,  these  high  proteid  consumers  are  apparently  quite 
able  to  utilize  the  vegetable  foods,  but  there  is  something  lack- 
ing in  such  a  dietary  which  the  body  has  great  need  of.  Is  it 
not  quite  possible,  as  already  suggested,  that  the  specific  na- 
ture of  the  proteid  counts  for  something  in  nutrition  ?  The 
question  cannot  be  answered  definitely  at  present,  but  there 
are  certain  facts  slowly  accumulating  which  make  the  question 
a  pertinent  one  in  this  connection. 

Thus,  it  is  becoming  evident,  as  was  pointed  out  in  an 
earlier  chapter,  that  the  many  proteid  substances  occurring 
in  the  animal  and  vegetable  kingdoms  are  more  or  less  unlike 
each  other  in  their  chemical  make-up.  They  yield  different 
decomposition  products,  or  the  same  products  in  widely  differ- 
ent proportion,  when  broken  down  by  the  action  of  hydrolyz- 
ing  agents ;  and  when  we  recall  that  the  digestive  enzymes  of 
the  body  convert  the  proteids  of  the  food  into  these  same 
end-products,  it  is  plain  that  in  the  assimilation  and  utiliza- 
tion of  the  proteid  foodstuffs  the  body  has  to  deal  with  these 
various  chemical  units.  Hence,  an  animal  suddenly  re- 
stricted to  a  dietary  in  which  all  of  the  proteid  is  furnished 
by  bread  might  be  seriously  incommoded,  either  by  the  excess 
of  certain  amino-acids  resulting  therefrom,  or  by  a  lack  of 
certain  other  end-products  to  which  its  body  is  accustomed. 
As  an  example,  we  may  take  the  three  typical  proteids  of  the 
wheat  kernel,  gliadin,  glutenin,  and  leucosin,  and  note  the 
very  striking  difference  in  the  proportion  of  certain  of  the 
decomposition  products  of  each,  as  reported  by  Osborne  and 
Clapp.1 


1  See  Osborne  and  Clapp :  The  Chemistry  of  the  Protein  Bodies  of  the 
Wheat  Kernel.    American  Journal  of  Physiology,  vol.  17,  p.  231. 


EFFECT  OF  LOW  PKOTEID  DIET 


259 


Gliadin. 

Glutenin. 

Leucosin. 

per  cent 
5.61 

per  cent 
5.95 

per  cent 
11.34 

o 

1.92 

2.75 

3.16 

4.72 

5.94 

37.33 

23.42 

6.73 

5.11 

4.01 

1.41 

Aspartic  ncid        ..... 

0.58 

0.91 

3.35 

1.20 

4.25 

3.34 

It  is  obvious  from  these  figures  that  the  three  proteids  of 
the  wheat  kernel  are  radically  different  from  each  other. 
Contrast,  for  example,  the  content  of  glutaminic  acid  in  gliadin 
with  the  amount  in  leucosin.  With  such  striking  differences 
in  chemical  make-up,  it  is  reasonable  to  assume  that  corre- 
sponding differences  in  physiological  action  or  food  values  may 
exist.  Further,  "in  respect  to  the  amount  of  these  amino- 
acids,  leucosin  more  nearly  resembles  the  animal  proteins  than 
the  seed  proteins  thus  far  examined,  and  in  this  connection  it 
is  interesting  to  note  that  leucosin  occurs  chiefly  if  not  wholly 
in  the  embryo  of  this  seed  and  is  probably  one  of  its  i  tissue  ' 
proteins,  in  contrast  to  the  '  reserve '  proteins  of  the  endosperm 
of  which  gliadin  and  glutenin  form  the  chief  part "  (Osborne 
and  Clapp).  In  other  words,  animal  proteids,  such  as  those 
of  meat,  are  characterized  like  leucosin  by  a  small  content  of 
glutaminic  acid  and  ammonia ;  while  leucin,  lysin,  aspartic 
acid,  and  arginm  are  relatively  more  abundant.  Until  we 
know  more  on  this  subject,  however,  any  broad  generalization 
would  be  out  of  place,  but  certainly  there  is  justification  for 
the  supposition  that  in  these  differences  in  chemical  constitu- 
tion are  to  be  found  explanation  of  some  of  the  peculiarities 
common  to  certain  varieties  of  proteid  food.  Wheat  flour, 


260  THE  NUTRITION  OF  MAN 

aside  from  its  starch,  is  composed  mainly  of  glutenin  and 
gliadin  with  their  large  content  of  glutaminic  acid.  Meat 
proteids,  on  the  other  hand,  like  leucosin,  contain  only  a 
small  fraction  of  this  acid,  and,  with  the  other  differences  in- 
dicated, meat  proteid  and  wheat  proteid  as  food  for  dogs  or 
other  high  proteid  consumers  may  reasonably  be  expected  to 
have  at  the  least  very  unequal  values.  And  if  we  go  a  step 
beyond  this  and  suppose  that  in  the  formation  of  true  tissue 
proteid  or  the  living  protoplasm  of  the  cell,  certain  of  these 
end-products  of  proteid  decomposition  are  absolutely  indis* 
pensable,  we  can  easily  picture  for  ourselves  a  dearth  of 
such  building  stones  in  the  long-continued  use  of  a  diet 
which  lacks  that  particular  proteid  from  which  the  necessary 
building  stones  can  be  split  off  in  adequate  number. 

It  has  been  said,  notably  by  Munk,  that  in  dogs  fed  for 
some  time  on  a  low  proteid  diet  there  is  a  diminished  power 
of  absorption  from  the  intestinal  tract,  associated  with 
weakened  digestion.  If  it  is  true  that  a  lowered  proteid  in- 
take results  in  a  diminished  utilization  of  the  ingested  food, 
that  efficiency  in  the  digestion  and  absorption  of  foodstuffs  is 
impaired,  it  can  only  be  interpreted  as  meaning  that  some  in- 
jurious influence  has  been  exerted  on  the  epithelial  cells  of  the 
intestine  or  the  adjacent  gland  cells.  We  have,  however, 
failed  to  find  any  evidence  of  deleterious  action  in  the  dogs  that 
we  have  experimented  with,  where  due  regard  was  paid  to  main- 
taining a  diet  suitable  for  the  physiological  needs  of  the  body. 
In  the  experiments  that  we  have  cited,  both  nitrogen  intake 
and  the  fuel  value  of  the  food  per  day  were  lower  than  in 
Munk's  experiments,  but  the  utilization  of  fat  and  proteid 
was  not  sensibly  affected.  The  following  tables  give  the  re- 
sults with  ten  dogs  (including  the  six  dogs  already  described) 
for  lengths  of  time  ranging  from  seven  to  twelve  months,  the 
periods  indicated  being  each  of  ten  days'  duration  and  occur- 
ring once  each  month.  In  the  first  table,  the  utilization  of 


EFFECT  OF  LOW  PROTEID  DIET 


261 


fat  is  shown,  the  figures  given  being  based  on  determina- 
tions of  the  amount  of  fat  contained  in  the  excrement, 
Knowing  the  amount  of  fat  in  the  daily  food  and  the  amount 
which  passed  through  the  intestine,  it  is  easy  to  calculate  the 
percentage  of  fat  utilized. 

UTILIZATION  OF  FAT  IN  PERCENTAGES. 


Periods. 

D 

JgS. 

1 

2 

3 

4 

5  . 

12 

13 

15 

17 

20 

1 

97 

96 

93 

97 

97 

96 

96 

98 

98 

95 

2 

96 

96 

98 

98 

98 

94 

95 

97 

98 

95 

3 

98 

97 

97 

99 

96 

97 

97 

98 

94 

98 

4 

98 

96 

97 

97 

96 

94 

95 

98 

97 

97 

6 

96 

.. 

94 

98 

97 

95 

95 

98 

97 

96 

6 

97 

98 

94 

98 

97 

96 

94 

97 

96 

97 

7 

97 

98 

98 

97 

96 

93 

95 

97 

98 

96 

8 

.. 

.. 

98 

96 

96 

96 

93 

97 

.. 

.. 

9 

.. 

.. 

98 

97 

98 

..* 

97 

98 

.. 

.. 

10 

.. 

.. 

98 

97 

98 

.. 

.. 

.. 

.. 

.. 

11 

.. 

.. 

97 

92 

97 

.. 

.. 

.. 

.. 

.. 

12 

97 

97 

It  is  perfectly  plain  from  these  results  that  there  was  no 
falling  off  in  the  utilization  of  fat;  the  percentage  amount 
digested  and  absorbed,  as  in  dogs  3  and  4,  was  just  as  large 
at  the  end  of  the  twelve  months'  experiment  as  at  the  begin- 
ning. Clearly,  a  so-called  low  nitrogen  intake  with  dogs  does 
not  lead  to  any  loss  of  power  in  the  utilization  of  the  fat  of 
the  food.  This  being  so,  it  is  equally  clear  that  the  argu- 
ments based  on  Munk's  results  in  this  direction,  and  applied 
to  man,  are  without  adequate  foundation. 


262 


THE  NUTRITION  OF  MAN 


UTILIZATION  OF  NITROGEN  IN  PERCENTAGES. 


Periods. 

D 

3gS. 

l 

2 

3 

4 

5 

12 

13 

15 

17 

20 

1 

95 

91 

92 

94 

91 

91 

90 

93 

92 

91 

2 

92 

94 

94 

95 

93 

90 

92 

96 

92 

87 

3 

91 

92 

90 

91 

88 

89 

86 

95 

89 

91 

4 

90 

85 

90 

92 

91 

82 

83 

91 

83 

93 

5 

90 

82 

88 

92 

86 

85 

84 

96 

91 

90 

6 

86 

87 

89 

83 

86 

89 

87 

94 

91 

86 

7 

87 

87 

90 

83 

87 

83 

88 

90 

93 

91 

8 

.  . 

90 

83 

84 

81 

89 

89 

9 

89 

87 

92 

87 

89 

.  • 

10 

.  . 

.  . 

93 

85 

94 

.  . 

.  . 

11 

.  . 

.  . 

93 

81 

86 

.  . 

.  . 

12 

89 

92 

The  figures  in  the  above  table  were  obtained  by  determin- 
ing the  amount  of  nitrogen  in  the  dried  excrement  from  the 
animals,  i.  e.  the  amount  that  passed  through  the  intestine  un- 
changed ; l  and  knowing  the  content  of  nitrogen  in  the  daily 
food,  the  percentage  of  unabsorbed  nitrogen  was  then  easily 
calculated,  after  which  by  simple  subtraction  the  percentage 
of  utilized  nitrogen  was  found.  At  first  glance,  it  would 
appear  that  as  the  experiments  proceeded  utilization  of  nitro- 
gen was  less  complete.  In  a  sense,  this  was  true,  but  it  was 
not  connected  with  any  impairment  of  the  digestive  or  absorp- 
tive powers  of  the  intestine.  It  must  be  remembered  that  in 


1  There  is  an  unavoidable  error  here,  since  the  excrement  contains  not  only 
undigested  food,  but  also  contains  some  nitrogenous  matter  derived  from  the 
secretions  of  the  intestine,  etc. 


EFFECT   OF  LOW  PROTEID  DIET  263 

the  earlier  periods  a  larger  proportion  of  the  ingested  nitrogen 
was  in  the  form  of  readily  digestible  meat,  but  as  the  latter 
was  reduced  in  amount  larger  proportions  of  vegetable  food 
were  introduced  in  order  to  maintain  the  desired  fuel  value, 
and  consequently  the  percentage  of  non-absorbable  nitrogen 
was  increased.  The  well-known  difference  in  the  availability 
of  animal  and  vegetable  proteid  has  already  been  referred  to 
in  other  connections ;  a  difference  due  not  so  much  to  any  inher- 
ent quality  in  the  digestibility  of  the  two  forms  of  proteid  as 
to  the  presence  of  cellulose  and  other  material  in  the  vegetable 
food  which  retards  in  some  measure  the  action  of  the  digestive 
juices.  To  this  cause  must  be  ascribed  the  slight  falling  off 
in  the  utilization  of  nitrogen  noticeable  in  most  of  the  experi- 
ments. If,  however,  the  figures  are  compared  with  those 
usually  obtained  on  a  diet  largely  vegetable  in  nature,  it  will 
be  seen  that  the  utilization  of  nitrogen  by  these  dogs  was  in 
no  sense  abnormal. 

These  experiments  on  the  influence  of  a  low  proteid  diet  on 
dogs,  as  a  type  of  high  proteid  consumers,  taken  in  their  en- 
tirety, afford  convincing  proof  that  such  animals  can  live  and 
thrive  on  amounts  of  proteid  and  non-nitrogenous  food  far 
below  the  standards  set  by  Munk  and  Rosenheim.  The  dele- 
terious results  reported  by  these  investigators  were  not  due 
to  the  effects  of  low  proteid  or  to  diminished  consumption  of 
non-nitrogenous  foods,  but  are  to  be  ascribed  mainly  to  non- 
hygienic  conditions,  or  to  a  lack  of  care  and  physiological 
good  sense  in  the  prescription  of  a  narrow  dietary  not  suited 
to  the  habits  and  needs  of  this  class  of  animals.  Further,  it  is 
obvious  that  the  more  or  less  broad  deductions  so  frequently 
drawn  from  the  experiments  of  Munk  and  Rosenheim,  espe- 
cially in  their  application  to  mankind,  are  entirely  unwar- 
ranted and  without  foundation  in  fact.  Our  experiments  offer 
satisfying  proof  that  not  only  can  dogs  live  on  quantities  of 
proteid  food  per  day  smaller  than  these  investigators  deemed 


264  THE   NUTKITION  OF  MAN 

necessary,  and  with  a  fuel  value  far  below  the  standard  adopted 
by  them ;  but,  in  addition,  that  these  animals  are  quite  able 
on  such  a  diet  to  gain  in  body-weight  and  to  lay  by  nitrogen, 
thereby  indicating  that  even  smaller  quantities  of  food  might 
suffice  to  meet  their  true  physiological  requirements. 

The  results  of  these  experiments  with  dogs,  which  we  have 
recorded  in  such  detail,  are  in  perfect  harmony  with  the  con- 
clusions arrived  at  by  our  experiments  and  observations  with 
man,  and  serve  to  strengthen  the  opinion,  so  many  times  ex- 
pressed, that  the  dietary  habits  of  mankind  and  the  dietary 
standards  based  thereon  are  not  always  in  accord  with  the  true 
physiological  requirements  of  the  body.  If  these  views  are 
correct,  and  the  facts  presented  seemingly  indicate  that  they 
are,  it  is  time  for  enlightened  people  to  give  heed  to  such  sug- 
gestions, that  their  lives  may  be  ordered  more  nearly  in  accord 
with  the  best  interests  of  the  body.  Physiological  economy 
in  nutrition  is  not  a  myth,  but  a  reality  full  of  promise  for  the 
welfare  of  the  individual  and  of  the  community  in  general. 
Ignorance  on  dietary  matters  should  give  place  to  an  intelli- 
gent comprehension  of  the  body's  needs,  and  an  adequate 
understanding  of  how  best  to  meet  the  legitimate  demands  of 
the  system  for  nourishment  under  given  conditions  of  life.  It 
is  said  that  more  than  half  the  earnings  of  the  working  people 
of  this  country  is  spent  for  food.  Here,  we  have  suggested 
another  form  of  economy  as  worthy  of  consideration ;  less  im- 
portant perhaps  than  that  which  relates  to  health  and  strength, 
but  still  calling  for  thoughtful  attention.  We  cannot  afford  to 
be  ignorant  of  these  things  ;  we  must  have  definite  knowledge 
of  the  actual  facts,  and  these  can  only  be  obtained  by  careful 
research  and  investigation. 

As  a  prominent  writer  on  nutrition  has  well  said,  "  The 
health  and  strength  of  all  are  intimately  dependent  upon  their 
diet.  Yet  most  people  understand  very  little  about  what  their 
food  contains,  how  it  nourishes  them,  whether  they  are  eco- 


EFFECT  OF  LOW  PEOTEID  DIET  265 

nomical  or  wasteful  in  buying  and  preparing  it  for  use,  and 
whether  or  not  the  food  they  eat  is  rightly  fitted  to  the  de- 
mands of  their  bodies.  The  result  of  this  ignorance  is  great 
waste  in  the  purchase  and  use  of  food,  loss  of  money,  and 
injury  to  health"  (At water).  We  all  recognize  the  general 
force  and  truth  of  this  statement,  but  there  is  a  surprising  lack 
of  appreciation  of  the  full  significance  of  what  is  involved 
thereby.  If  it  is  true  that  the  demands  of  the  body  for  pro- 
teid  food  —  which  of  all  foods  is  the  most  expensive  —  are 
fully  met  by  an  amount  equal  to  one-half  that  ordinarily  con- 
sumed, and  that  health  and  strength  are  more  satisfactorily 
maintained  thereby,  it  is  easy  to  see  how  the  acquisition  of 
dietary  habits  leading  to  consumption  of  food  in  harmony 
with  physiological  needs  will  result  in  a  fruitful  twofold 
economy;  viz.,  economy  in  expenditure,  and  of  still  greater 
moment,  economy  in  the  activities  of  the  body  by  which  food 
and  its  waste  products  are  cared  for. 


CHAPTER  VIII 

PRACTICAL  APPLICATIONS  WITH   SOME 
ADDITIONAL  DATA 

TOPICS  :  Proper  application  of  the  results  of  scientific  research  helpful 
to  mankind.  Dietary  habits  should  be  brought  into  conformity  with 
the  true  needs  of  the  body.  The  peculiar  position  of  proteid  foods 
emphasized.  The  evil  effects  of  overeating.  What  the  new  dietary 
standards  really  involve.  The  actual  amounts  of  foodstuffs  required. 
Relation  of  nutritive  value  to  cost  of  foods.  The  advantages  of  sim- 
plicity in  diet.  A  sample  dietary  for  a  man  of  70  kilograms  body- 
weight.  A  new  method  of  indicating  food  values.  Moderation  in 
the  daily  dietary  leads  toward  vegetable  foods.  The  experiments  of 
Dr.  Neumann.  The  value  of  fruits  as  food.  The  merits  of  animal 
and  vegetable  proteids  considered  in  relation  to  the  bacterial  processes 
in  the  intestine.  A  notable  case  of  simplicity  in  diet.  Intelligent 
modification  of  diet  to  the  temporary  needs  of  the  body.  Diet  in 
summer  and  winter  contrasted.  Value  of  greater  protection  to  the 
kidneys.  Conclusion. 

KNOWLEDGE  has  value  in  proportion  to  the  benefit  it 
confers,  directly  or  indirectly,  on  the  human  race. 
Every  new  scientific  fact  or  principle  brought  to  light  prom- 
ises help  in  the  understanding  of  Nature's  laws,  and  when 
rightly  interpreted  and  properly  applied  is  sure  to  aid  in  the 
advancement  and  prosperity  of  the  individual  and  of  the 
community.  Proper  methods  of  living,  economical  adjust- 
ment of  the  intake  to  the  varying  needs  of  the  body,  avoid- 
ance of  excessive  waste  of  foodstuffs  and  of  energy,  are  all 
desirable  precepts,  which  rational  people  presumably  are  in- 
clined to  follow  so  far  as  their  knowledge  and  understanding 
of  the  subject  will  permit.  Here,  as  elsewhere,  false  teaching 


PEACTICAL  APPLICATIONS  26T 

may  be  exceedingly  mischievous  and  lead  to  costly  errors  ; 
while  blind  reliance  upon  customs,  instinct,  and  superstitions 
is  hardly  in  keeping  with  twentieth-century  progress. 

Modern  scientific  methods  should  give  us  help  in  dietetics, 
as  in  other  branches  of  hygiene  and  practical  medicine.  A 
few  short  years  ago,  diphtheria  was  a  scourge  which  brought 
misery  to  many  a  home,  for  there  was  at  hand  no  adequate 
means  of  combating  the  disease ;  but  scientific  research  has 
given  us  new  light,  and  placed  at  our  command  a  weapon  of 
inestimable  value.  Do  we  hesitate  to  use  it  when  the  occasion 
arises,  because  it  happens  to  be  out  of  keeping  with  old-time 
customs  and  traditions  ?  No,  we  recognize  the  possibility  of 
help,  and  as  the  need  is  urgent  we  turn  to  it  quickly,  with 
hope  and  thankfulness  that  scientific  progress  has  opened  up 
a  pathway  of  escape  from  a  threatened  calamity. 

Not  many  years  ago  we  drank  freely  of  such  water  as  was 
at  hand,  without  realization  of  danger  from  bacteria  or  disease 
germs,  looking  on  epidemics  of  typhoid  fever  perhaps  as  a  visi- 
tation of  Divine  Providence,  in  punishment  of  our  many  sins 
and  to  be  borne  meekly  and  with  resignation.  But  all  this 
has  changed  through  the  researches  of  bacteriologists  and 
chemists ;  scientific  facts  of  the  utmost  importance  have  been 
clearly  established ;  a  classification  of  water-borne  diseases  has 
been  adopted,  and  we  realize  fully  that  diseases  of  this  order 
can  be  kept  from  our  doors  by  proper  precautions  applied  to 
our  water  supply.  To-day,  epidemics  of  typhoid  fever  are 
traceable  solely  to  the  ignorance  or  carelessness  of  the  individ- 
ual or  of  the  commonwealth,  and  the  exemption  which  we  of 
the  present  generation  have  from  this  class  of  diseases  is 
directly  due  to  the  application  of  precautionary  measures 
based  on  the  information  furnished  by  scientific  investigation. 
It  is  proper  for  us  to  use  caution  in  the  acceptance  of  new  ideas, 
but  not  that  form  of  caution  which  refuses  change  on  the 
ground  that  what  has  been  is  sufficiently  good  for  the  present 


268  THE  NUTRITION  OF  MAN 

and  the  future.  The  point  of  view  is  ever  changing  with 
advance  of  knowledge,  and  it  is  not  profitable  to  exclude  op- 
portunities for  improvement  in  personal  hygiene  and  general 
good  health,  any  more  than  in  other  matters  that  affect  the 
prosperity  of  the  individual  or  the  community. 

Dietary  habits  should  be  brought  into  conformity  with  the 
true  needs  of  the  body.  Excessive  consumption  of  proteid 
food,  especially,  should  be  avoided  on  the  ground  that  it  is 
not  only  unnecessary  and  wasteful,  but  is  liable  to  bring 
penalties  of  its  own,  most  undesirable  and  wholly  uncalled 
for.  We  may,  perhaps,  accept  these  statements  at  their  full 
value,  and  yet  have  a  shadow  of  doubt  in  our  minds  as  to 
whether,  after  all,  dietary  customs  do  not  harmonize  sufficiently 
at  least  with  true  nutritive  requirements.  All  the  data  that 
we  have  presented  in  the  preceding  chapters,  however,  have 
seemingly  given  a  positive  answer  to  such  doubts,  and  indicate 
quite  clearly  that  the  results  of  scientific  study  are  opposed  to 
the  prevailing  dietary  standards,  especially  as  regards  proteid 
food.  As  the  celebrated  physiologist  Bunge  has  expressed  it, 
"The  necessity  for  a  daily  consumption  of  100  grams  of  pro- 
teid is  incomprehensible,  so  long  as  we  do  not  know  of  any 
function  of  the  body  in  the  performance  of  which  the  chemical 
potential  energies  of  the  destroyed  proteid  are  used  up." 

Perfectly  trustworthy  evidence  is  at  hand  showing  that  the 
needs  of  the  body  for  potential  energy  can  be  fully  met,  and 
indeed  are  more  advantageously  met,  by  the  non-nitrogenous 
foods,  carbohydrates  and  fats.  The  energy  of  muscle  work, 
as  we  have  seen,  comes  preferably  from  the  breaking  down  of 
non-nitrogenous  material,  so  that  there  is  no  special  call  for 
proteid  in  connection  with  increased  muscular  activity.  In 
fact,  it  would  appear  that  the  need  for  proteid  food  by  man  is 
limited  to  the  requirements  of  growth  and  development,  re- 
inforced by  the  amount  called  for  in  that  form  of  tissue 
exchange  which  we  have  emphasized  under  the  term  "en- 


PRACTICAL  APPLICATIONS  269 

dogenous  proteid  metabolism,"  or  true  tissue  metabolism. 
To  be  sure,  there  must  be  a  certain  reserve  of  proteid,  avail- 
able in  case  of  emergency,  but  this  is  easily  established  with- 
out resorting  to  excessive  feeding. 

The  peculiar  position  which  proteid  foods  occupy  in  man's 
dietary  naturally  make  them  the  central  figure,  around  which 
the  other  foods  are  grouped.  No  other  form  of  food  can  take 
the  place  of  proteid ;  a  certain  amount  is  needed  each  day  to 
make  good  the  loss  of  tissue  material  broken  down  in  endoge- 
nous katabolism,  and  consequently  our  choice  and  combi- 
nation of  the  varied  articles  of  diet  made  use  of  should  be 
regulated  by  the  amount  of  proteid  they  contain.  But  while 
proteid  foods  occupy  this  commanding  position,  it  is  not  nec- 
essary or  desirable  that  they  should  exceed  the  other  food- 
stuffs in  amount,  or  indeed  approach  them  in  quantity.  We 
must  be  ever  mindful  of  the  fact,  so  many  times  expressed, 
that  proteid  does  not  undergo  complete  oxidation  in  the  body 
to  simple  gaseous  products  like  the  non-nitrogenous  foods, 
but  that  there  is  left  behind  a  residue  of  non-combustible 
matter  —  solid  oxidation  products  —  which  are  not  so  easily 
disposed  of.  In  the  forceful  language  of  another,  "  The  com- 
bustion of  proteid  within  the  organism  yields  a  solid  ash 
which  must  be  raked  down  by  the  liver  and  thrown  out  by 
the  kidneys.  Now  when  this  task  gets  to  be  over-laborious, 
the  laborers  are  likely  to  go  on  strike.  The  grate,  then,  is 
not  properly  raked ;  clinkers  form,  and  slowly  the  smothered 
fire  glows  dull  and  dies  "  (Curtis). 

Even  though  no  such  dire  fate  overtakes  one,  the  penalties 
of  excessive  proteid  consumption  are  found  in  many  ills,  for 
which  perhaps  the  victim  seeks  in  vain  a  logical  explanation ; 
gastro-intestinal  disturbance,  indigestion,  intestinal  toxaemia, 
liver  troubles,  bilious  attacks,  gout,  rheumatism,  to  say  nothing 
of  many  other  ailments,  some  more  and  some  less  serious,  are 
associated  with  the  habitual  overeating  of  proteid  food.  But 


270  THE  NUTRITION  OF  MAN 

excessive  food  consumption  is  by  no  means  confined  to  the 
proteid  foodstuffs  ;  general  overfeeding  is  a  widespread  evil, 
the  marks  of  which  are  to  be  detected  on  all  sides,  and  in  no 
uncertain  fashion.  One  of  the  most  common  signs  of  exces- 
sive food  consumption  is  the  tendency  toward  obesity,  a  con- 
dition which  is  distinctly  undesirable  and  may  prove  decidedly 
injurious.  Undue  accumulation  of  fat  is  not  only  a  mechan- 
ical obstacle  to  the  proper  activity  of  the  body  as  a  whole, 
but  it  interferes  with  the  freedom  of  movement  of  such 
muscular  organs  as  the  heart  and  stomach,  thereby  interposing 
obstacles  to  the  normal  action  of  these  structures.  Further, 
whenever  undue  fat  formation  is  going  on  in  the  body,  there 
is  the  ever  present  danger  that  the  lifeless  fat  may  replace 
the  living  protoplasm  of  the  tissue  cells  and  so  give  rise  to  a 
condition  known  as  "  fatty  degeneration."  While  a  super- 
abundance of  fat  in  the  body  is  a  sure  telltale  of  overeating, 
the  absence  of  obesity  is  by  no  means  an  indication  that  excess 
of  food  is  being  avoided.  There  is  here,  in  man  as,  in  animal 
kind,  much  idiosyncrasy ;  some  persons,  especially  those  en- 
dowed with  a  long  and  large  frame,  tend  to  keep  thin  even 
though  they  eat  excessively,  while  others  grow  fat  much 
more  readily.  As  a  well-known  physician  has  expressed  it, 
"  In  the  one  case,  the  subject  burns,  instantly  and  mercilessly, 
every  stick  of  fuel  delivered  at  his  door,  whether  or  not  he 
needs  the  resulting  hot  fire  roaring  within,  while  the  other, 
miser-like,  hoards  the  rest  in  vast  piles,  filling  the  house  from 
cellar  to  garret." 

Temperance  in  diet,  like  temperance  in  other  matters,  leads 
to  good  results,  and  our  physiological  evidence  points  out 
plainly,  like  a  signpost  all  can  read,  that  there  is  no  demand 
on  the  part  of  the  body  for  such  quantities  of  food  as  custom 
and  habit  call  for.  Healthf ulness  and  longevity  are  the  prizes 
awarded  for  the  successful  pursuance  of  a  temperate  life, 
modelled  in  conformity  with  Nature's  laws.  Intemperance,  on 


PRACTICAL   APPLICATIONS  271 

the  other  hand,  in  diet  as  in  other  matters,  is  equally  liable 
to  be  followed  by  disaster.  A  physician  of  many  years'  ex- 
perience, with  opportunities  for  observation  among  different 
classes  of  people,  has  written,  "  that  overeating  tends  to 
shrink  the  span  of  life  in  proportion  as  it  expands  the  liver  is 
demonstrable  both  directly  and  indirectly.  Let  any  actuaiy 
of  life-insurance  be  asked  his  experience  with  heavy-weight 
risks,  where  the  waist  measures  more  than  the  chest,  and  the 
long-drawn  face  of  the  businessman,  at  memory  of  lost  dollars, 
will  make  answer  without  need  of  words.  Then  let  be  noted 
the  physique  of  the  blessed  ones  that  attain  to  green  old  age, 
and,  in  nine  cases  out  of  ten,  spry  old  boys  —  no  disparage- 
ment, but  all  honor  in  the  phrase  —  will  be  found  to  be 
modelled  after  the  type  of  octogenarian  Bryant  or  nonoge- 
narian  Bancroft  —  the  whitefaced,  wiry,  and  spare,  as  con- 
trasted with  the  red-faced,  the  pursy,  and  the  stout.  It  is 
true,  as  has  already  been  mentioned,  that  in  old  age  much  of 
an  adventitious  obesity  is  absorbed  and  disappears,  but  the 
Bryant-Bancroft  type  is  that  of  a  subject  who  never  has  been 
fat  at  all.  And  just  such  is  preeminently  the  type  that  rides 
easily  past  the  fourscore  mark,  reins  well  in  hand,  and  good 
for  many  another  lap  in  the  race  of  life."  l 

With  these  thoughts  before  us,  we  may  consider  briefly 
just  what  is  involved  in  these  new  dietary  standards  that  aim 
to  conform  more  closely  with  actual  body  needs.  Referring 
at  first  to  proteid  food,  it  may  be  wise  to  again  emphasize  the 
fact  that  the  weight  of  the  body,  i.  e.,  the  weight  of  the  pro- 
teid-containing  tissues,  as  contrasted  with  excessive  fat  accu- 
mulation, is  one  of  the  important  factors  not  to  be  overlooked 
when  determining  the  dietary  needs  of  a  given  individual. 
As  must  be  perfectly  clear,  from  all  that  has  been  said,  the 
man  of  170  pounds'  body-weight  has  more  proteid  tissue  to 


i  Edward  Curtis,  M.D. :  Nature  and  Health,  p.  70.      Henry  Holt  &  Com- 
pany, New  York,  1906. 


272  THE  NUTRITION  OF  MAN 

nourish  than  the  man  of  130  pounds'  weight,  and  consequently 
what  will  satisfy  the  requirements  of  the  latter  individual  will 
not  suffice  for  the  former.  We  must  understand  distinctly 
that  no  general  statement  can  be  made  applicable  to  mankind 
at  large,  but  due  consideration  must  be  given  to  the  size  and 
weight  of  the  individual  structure.  We  have  found  that  the 
average  need  for  proteid  food  by  adults  is  fully  met  by  a  daily 
metabolism  equal  to  an  exchange  of  0.12  gram  of  nitrogen 
per  kilogram  of  body-weight.  This  means  a  katabolism  of 
three-fourths  of  a  gram  of  proteid  matter  daily,  per  kilogram. 

Remembering,  however,  that  the  intake  of  proteid  food  must 
be  somewhat  in  excess  of  the  actual  proteid  katabolism,  since 
not  all  of  the  proteid  of  the  food  is  available,  and  as  this  is  a 
variable  amount  depending  upon  the  proportion  of  animal  and 
vegetable  foods  with  their  different  degrees  of  digestibility 
and  availability,  we  may  place  the  required  intake  of  proteid 
at  0.85  gram  per  kilogram  of  body-weight,  still  keeping  to 
maximum  figures  for  safety's  sake.  Hence,  for  a  man  weigh- 
ing 70  kilograms  or  154  pounds,  there  would  be  required 
daily  59.5  grams  —  say  60  grams  —  of  proteid  food  to  meet 
the  needs  of  the  body.  These  are  perfectly  trustworthy 
figures,  with  a  reasonable  margin  of  safety,  and  carrying  per- 
fect assurance  of  being  really  more  than  sufficient  to  meet  the 
true  wants  of  the  body ;  adequate  to  supply  all  physiological 
demands  for  reserve  proteid,  and  able  to  cope  with  the  erratic 
requirements  of  personal  idiosyncrasies.  It  will  be  observed 
that  such  an  intake  of  proteid  food  daily  is  equal  to  one-half 
the  Yoit  standard  for  a  man  of  this  weight,  while  it  is  still 
further  below  the  Atwater  standard  and  far  below  the  common 
practices  of  the  majority  of  mankind  in  Europe  and  America, 
as  indicated  by  the  published  dietary  studies. 

It  may  not  be  out  of  place  to  state  at  this  point  that  in  the 
writer's  opinion  the  use  of  the  terms  "  standard  diet "  and 
"dietary  standards,"  etc.,  is  objectionable,  since  such  usage 


PRACTICAL  APPLICATIONS  273 

seems  to  demand  a  certain  degree  of  defmiteness  in  the  daily 
diet  for  which  there  is  no  justification.  As  in  the  use  of  the 
term  "normal  diet,"  there  is  danger  of  misinterpretation,  and 
of  the  assumption  that  dietary  habits  should  be  regulated 
strictly  in  accord  with  certain  set  principles.  This  I  believe 
to  be  altogether  wrong ;  there  should  be,  on  the  contrary,  full 
latitude  for  individual  freedom,  but  freedom  governed  by  an 
intelligence  that  appreciates  the  significance  of  scientific  fact 
and  is  willing  to  mould  custom  and  habit  into  accord  with 
them.  What  is  needed  to-day  is  not  so  much  an  acceptance 
of  the  view  that  man  requires  daily  0.85  gram  of  proteid  per 
kilogram  of  body- weight,  as  a  full  appreciation  of  the  general 
principle,  which  our  definite  figures  have  helped  to  work  out, 
that  the  requirements  of  the  body  for  proteid  food  are  far 
below  the  customary  habits  of  mankind,  and  that  there  is  both 
economy  and  gain  in  various  directions  to  be  derived  by  follow- 
ing the  general  precepts  which  this  view  leads  to.  In  other 
words,  there  is  no  advantage,  but,  on  the  contrary,  much  bother 
and  worriment,  in  attempting  to  follow  out  in  practice  the 
details  of  our  more  or  less  exact  physiological  experiments. 

The  general  teaching  which  they  afford,  however,  can  be 
adopted  and  put  in  practice  in  our  daily  lives,  without  striv- 
ing to  follow  too  closely  the  so-called  standards  which  our 
experiments  have  led  to.  Again,  the  sample  dietaries  adopted 
in  our  experiments  have  no  special  virtue,  aside  from  the 
general  principle  they  teach  that  simple  foods  are  quite  ade- 
quate for  the  nourishment  of  the  body,  and  that  the  amount 
of  nitrogen  or  proteid  they  contain  was  sufficient  to  meet  the 
demands  of  the  particular  individuals  consuming  it.  Broad- 
ening intelligence  on  matters  of  food  composition  is  called  for 
on  all  sides,  and  as  this  is  acquired  together  with  due  appre- 
ciation of  the  relative  nutritive  values  of  proteid,  fat,  and  car- 
bohydrate, there  is  placed  at  our  command  the  power  of 
intelligent  discrimination,  with  the  ability  to  apply  the  prin- 

18 


274  THE  NUTRITION   OF  MAN 

ciples  set  forth  in  our  own  way,  in  harmony  with  personal 
likes  and  dislikes. 

To  the  majority  of  us,  not  very  familiar  with  the  percentage 
composition  of  ordinary  food  materials,  and  unaccustomed  to 
the  weighing  of  food  in  grams,  the  figures  given  from  time  to 
time  may  have  failed  to  convey  a  very  definite  impression  re- 
garding the  actual  amounts  of  the  various  foods  made  use  of. 
Further,  our  ideas  concerning  the  bulk  of  many  of  the  com- 
mon articles  of  food  necessary  to  furnish  the  60  grams  of  pro- 
teid  required  daily  by  a  man  of  TO  kilograms  body- weight 
may  be  somewhat  hazy.  The  following  table,  however,  will 
be  of  service  in  this  direction: 

SIXTY  GRAMS  OF  PROTEID  ARE   CONTAINED  IN 

Fuel  Value* 

One-half  pound  fresh  lean  beef,  loin 308  calories 

Nine  hens'  eggs 720 

Four-fifths  pound  sweetbread 660 

Three-fourths  pound  fresh  liver 432 

Seven-eighths  pound  lean  smoked  bacon 1820 

Three-fourths  pound  halibut  steak 423 

One-half  pound  salt  codfish,  boneless 245 

Two-and  one- fifth  pounds  oysters,  solid 506 

One-half  pound  American  pale  cheese 1027 

Four  pounds  whole  milk  (two  quarts) 1300 

Five-sixths  pound  uncooked  oatmeal 1550 

One  and  one-fourtli  pounds  shredded  wheat 2125 

One  pound  uncooked  macaroni 1665 

One  and  one-third  pounds  white  wheat  bread 1520 

One  and  one-fourth  pounds  crackers 2381 

One  and  two-thirds  pounds  flaked  rice 2807 

Three-fifths  pound  dried  beans       963 

One  and  seven-eighths  pounds  baked  beans 1125 

One-half  pound  dried  peas 827 

One  and  eleven-twelfths  pounds  potato  chips 5128 

Two-thirds  pound  almonds 2020 

Two-fifths  pound  pine  nuts,  pignolias 1138 


1  Fuel  value  of  the  quantity  needed  to  furnish  the  sixty  grams  of  proteid. 


PRACTICAL  APPLICATIONS  275 

Fuel  Value 

One  and  two-fifths  pounds  peanuts 3584  calories 

Ten  pounds  bananas,  edible  portion 4600 

Ten  pounds  grapes 4500 

Eleven  pounds  lettuce 990 

Fifteen  pounds  prunes 5550 

Thirty-three  pounds  apples 9570 

The  figures  in  this  table  are  instructive  in  many  ways. 
First,  it  is  to  be  noted  that  the  daily  proteid  requirement  of 
sixty  grams  can  be  obtained  from  one-half  pound  of  lean  meat 
(uncooked),  of  which  the  loin  steak  is  a  type.  Subject  to  some 
variations  in  content  of  water,  an  equivalent  weight  of  lean 
flesh  of  any  variety,  lamb,  veal,  poultry,  etc.,  will  furnish 
approximately  the  same  amount  of  proteid.  With  fish,  such 
as  halibut  steak,  and  with  liver,  three-quarters  of  a  pound  are 
required ;  while  with  sweetbreads,  four-fifths  of  a  pound  are 
needed  to  furnish  the  requisite  amount  of  proteid.  Of  salt 
codfish,  one-half  pound  will  provide  the  same  amount  of  pro- 
teid as  an  equivalent  weight  of  fresh  beef ;  while  with  lean 
smoked  bacon  the  amount  rises  to  seven-eighths  of  a  pound. 
Among  the  vegetable  products,  it  is  to  be  observed  that  dried 
peas  and  beans,  almonds  and  pine  nuts,  are  as  rich  in  proteid 
as  the  above-mentioned  animal  foods,  essentially  the  same 
weights  being  called  for  to  provide  the  daily  requirement  of 
proteid.  The  same  is  true  of  cheese,  the  variety  designated 
having  such  a  composition  that  one-half  pound  is  the  equiv- 
alent, so  far  as  the  content  of  proteid  is  concerned,  of  a  like 
amount  of  fresh  beef.  We  must  not  be  unmindful  of  the  fact 
previously  mentioned,  however,  that  there  are  differences  in 
digestibility  among  these  various  foodstuffs  which  tend  to 
lower  somewhat  the  availability  of  the  vegetable  products, 
also  of  the  cheese,  thereby  necessitating  a  slight  increase 
in  the  amount  of  these  foods  required  to  equal  the  value  to 
the  body  of  lean  meat. 

Secondly,  passing  to  the  other  extreme  in  our  list,  we  find 


276  THE  NUTRITION  OF  MAN 

indicated  types  of  foods  exceedingly  poor  in  proteid,  such  as 
the  fruits ;  notably,  bananas,  grapes,  prunes,  apples,  etc.,  also 
lettuce,  and  in  less  degree  potatoes.  These  are  the  kinds  of 
food  that  may  legitimately  attract  by  their  palatability,  but  do 
not  add  materially  to  our  intake  of  proteid  even  when  con- 
sumed in  relatively  large  amounts.  Thirdly,  we  see  clearly 
indicated  a  radical  difference  between  the  animal  foods  and 
those  of  vegetable  origin,  in  that  with  the  former  the  fuel 
value  of  the  quantity  necessary  to  furnish  the  sixty  grains  of 
proteid  is  very  small,  as  compared  with  a  like  amount  of  the 
average  vegetable  product.  One-half  pound  of  lean  meat,  for 
example,  with  its  60  grams  of  proteid,  has  a  fuel  value  of 
only  308  calories,  while  two-thirds  of  a  pound  of  almonds 
has  a  fuel  value  of  2020  calories,  and  one-half  pound  of  dried 
peas  827  calories.  Naturally,  this  is  mainly  a  question  of 
the  proportion  of  fat  or  oil  present.  With  fat  meat,  as  in 
bacon,  the  calorific  value  rises  in  proportion  to  increase  in 
the  amount  of  fat,  the  proteid  decreasing  in  greater  or  less 
measure. 

The  main  point  to  be  emphasized  in  this  connection,  how- 
ever, is  that  a  high  proteid  animal  food,  like  lean  meat,  eggs, 
fish,  etc.,  obviously  cannot  alone  serve  as  an  advantageous 
food  for  man.  We  see  at  once  the  philosophy  of  a  mixed 
diet.  Let  us  assume  that  our  average  man  of  70  kilograms 
body-weight  needs  daily  2800  calories.  On  this  assumption, 
if  he  were  to  depend  entirely  upon  lean  beef  for  his  suste- 
nance, he  would  require  daily  four  and  a  half  pounds  of 
such  meat,  which  amount  would  furnish  nine  times  the 
quantity  of  proteid  needed  by  his  system.  The  same  would 
be  more  or  less  true  of  other  kindred  animal  products.  On 
the  other  hand,  certain  vegetable  foods  on  our  list,  such  as 
flaked  rice,  crackers,  and  shredded  wheat,  contain  proteid, 
with  carbohydrate  and  fat,  in  such  proportion  that  the  energy 
requirement  would  be  met  essentially  by  the  same  quantity  as 


PRACTICAL  APPLICATIONS  277 

served  to  furnish  the  necessary  proteid.  Passing  to  the  other 
extreme  among  the  vegetable  products,  as  in  potatoes  and 
bananas,  for  example,  we  find  fuel  value  predominating  largely 
over  proteid  content.  The  ideal  diet,  however,  is  found  in  a 
judicious  admixture  of  foodstuffs  of  both  animal  and  vegetable 
origin.  Wheat  bread,  reinforced  by  a  little  butter  or  fat 
bacon  to  add  to  its  calorific  value,  shredded  wheat  with  rich 
cream,  crackers  with  cheese,  bread  and  milk,  eggs  with  bacon, 
meat  with  potatoes,  etc.;  the  common,  every-day  household 
admixtures,  provide  combinations  which  can  easily  be  made  to 
accord  with  true  physiological  requirements.  The  same  may 
be  equally  true  of  the  more  complicated  dishes  evolved  by  the 
high  art  of  modern  cookery. 

Lastly,  our  table  throws  light  upon  certain  questions  of 
household  economy.  The  cost  of  foods  is  regulated  mainly 
not  by  the  value  of  the  nutrients  contained  therein,  but 
by  other  factors  of  quite  a  different  nature.  Relationship 
between  supply  and  demand  naturally  counts  here  as  in 
other  directions,  but  our  demand  is  liable  to  be  based  not 
upon  food  values,  but  rather  upon  delicacy  of  flavor,  pala- 
tability,  and  other  kindred  fancies,  some  real  and  some  imagi- 
nary. Ordinary  crackers  can  be  purchased  for  ten  cents  a 
pound,  but  if  we  desire  a  little  stronger  flavor  of  salt  and  a 
special  box  to  hold  them,  we  pay  eighteen  cents  a  pound. 
Rolled  very  thin  and  thus  made  more  delicate,  they  cost 
twenty-five  cents,  while  sold  under  a  special  name  and  perhaps 
tied  with  a  blue  ribbon  they  cost  thirty-five  cents  a  pound. 
Their  nutritive  value  per  pound  is  the  same  in  all  cases,  but 
we  pay  something  for  the  increased  labor  of  preparation  and 
a  good  deal  for  the  added  attractiveness  to  eye  and  palate. 
We  pay  twenty-two  cents  a  pound  for  round  steak,  thirty-two 
cents  for  loin  steak,  and  seventy- five  cents  a  pound  for  sweet- 
breads, the  high  price  of  the  latter  being  regulated  by  the 
relative  scarcity  of  the  article  and  not  by  its  food  value.  As 


278  THE  NUTRITION   OF  MAN 

our  table  indicates,  the  real  value  of  sweetbread  as  a  source  of 
proteid  is  only  a  little  more  than  half  that  of  lean  beef.  Its 
fuel  value,  however,  is  somewhat  more  than  that  of  beef,  but 
a  little  fat  added  to  the  latter  will  more  than  compensate  and 
at  a  trifling  cost.  When  we  can  afford  it,  we  pay  the  in- 
creased price  for  sweetbreads  simply  because  their  delicacy  and 
flavor  are  attractive  to  us.  We  should  not  do  it  under  the 
mistaken  idea  that  we  are  indulging  in  a  highly  nutritive 
article  of  food,  for  as  a  matter  of  fact  it  is  not  only  less  nutri- 
tive than  a  corresponding  weight  of  lean  beef,  but  in  addi- 
tion it  possesses  certain  qualities,  in  its  high  purin-content, 
that  are  a  menace  to  good  health  if  indulged  in  too  freely. 

Where  expense  must  be  carefully  guarded,  or  where  the  con- 
dition of  the  family  purse  is  such  that  conflicting  demands 
must  be  intelligently  considered  in  order  to  insure  wise  ex- 
penditure and  the  greatest  permanent  good  of  the  many,  it  is 
well  to  remember  that  price  is  no  guarantee  whatever  of  real 
nutritive  value.  Two  quarts  of  milk  will  furnish  half  the 
daily  fuel  requirement  of  our  average  man  and  the  entire 
proteid  requirement,  while  its  cost  is  only  sixteen  cents. 
Reinforced  by  a  pound  loaf  of  wheat  bread,  the  energy  re- 
quirement for  the  day  would  be  fully  met,  with  surplus  ni- 
trogen to  store  up  for  future  needs,  and  at  an  additional  cost 
of  only  ten  cents.  A  mixture  in  this  proportion,  however, 
would  not  be  strictly  physiological,  since  it  is  wasteful  of  pro- 
teid, but  it  may  serve  to  illustrate  the  point.  A  better  illus- 
tration is  found  in  an  admixture,  quite  adequate  to  supply  the 
daily  needs  of  our  average  man,  both  for  proteid  and  energy, 
composed  of  one-quarter  of  a  pound  of  lean  beef,  two-thirds  of 
a  pound  of  bread,  and  half  a  pound  of  butter,  and  at  a  total 
cost  not  to  exceed  thirty  cents.  The  contrast  of  such  prices 
with  what  is  so  commonly  paid  for  table  delicacies  is  some- 
what striking;  it  could  be  made  still  more  so  by  drawing 
upon  many  common  vegetable  foods,  rich  alike  in  proteid  and 


PEACTICAL  APPLICATIONS  279 

in  fuel  value,  the  cost  of  which  is  even  less  than  the  simple 
food  mixtures  just  referred  to.  It  is  not  necessary,  however, 
to  enlarge  upon  this  question ;  it  is  sufficient  to  merely  em- 
phasize the  fact  that  the  exaggerated  demand  of  our  present 
generation  for  dietetic  luxuries  is  leading  us  far  away  from 
the  proverbially  simple  life  of  our  forefathers,  and  without 
adding  in  any  way  to  the  effectiveness  of  the  daily  diet.  On 
the  contrary,  it  is  in  part  responsible  for  the  high  proteid  con- 
sumption of  the  present  day,  with  its  attendant  evils,  and  in- 
volves a  large  and  unnecessary  expenditure  without  adequate 
return.  The  wants  of  the  body  for  food  are  far  more  advan- 
tageously met  by  a  simple  dietary,  moderate  in  amount  and  at 
an  expense  comparatively  slight. 

A  recent  writer,1  in  the  "  British  Medical  Journal, "  a 
practitioner  of  medicine  in  the  Highlands  of  Scotland,  has 
said  that  these  are  "  facts  of  common  experience  in  the  High- 
lands of  Scotland,  and  probably  among  the  peasantry  of  other 
countries  also,  where  the  old  beliefs  and  customs  have  not  too 
readily  given  way  to  the  luxuries  of  civilization.  Oatmeal  in 
one  form  or  another  is  a  daily  ingredient  in  the  diet  of  a 
Highland  peasant.  The  potato  also  is  a  staple  food,  and  is 
consumed  in  large  quantities  with  salt  herring  or  other  fish, 
and  perhaps  in  some  cases  salt  mutton  or  pork.  Milk  and 
eggs  are  used  by  most.  The  growing  consumption  of  tea, 
however,  and  the  increasing  relish  for  sweets,  candy,  pastry, 
and  biscuits,  threaten  to  destroy  the  old  way  of  living.  A 
typical  day's  diet  for  a  crofter  or  fisherman  who  still  believes 
in  the  traditional  diet  would  be  somewhat  like  this : 

Breakfast.  —  Oatmeal  porridge  or  brose  with  milk  ;  bread,  butter,  and  tea. 
Dinner.  —  Potatoes  galore  and  herrings,  or  other  salt  fish. 
Supper.  — Porridge  and  milk,  or  oat  bread  and  cheese,  and  tea. 

"  I  have  often  been  assured  by  shepherds  that  they  could 
work  all  day  <  on  the  hill '  after  a  breakfast  of  oatmeal  brose 

1  Aran  Coirce  :  British  Medical  Journal,  April  7,  1906,  p.  829. 


280  THE  NUTRITION  OF  MAN 

and  milk,  without  fatigue  and  without  feeling  hungry,  return- 
ing in  the  evening  to  partake  of  a  dish  of  broth,  potatoes,  and 
salt  mutton.  In  these  diets,  proteid  forms  a  very  small  pro- 
portion, and  yet  a  hardier  race  than  these  shepherds  and  fisher- 
men cannot  be  found."  It  should  be  added  that  "  brose " 
consists  of  a  few  handfuls  of  oatmeal,  to  which  is  added  boil- 
ing water,  the  mixture  being  stirred  vigorously  and  placed 
for  a  few  minutes  near  the  fire.  It  is  then  eaten  with  milk, 
or  better,  with  cream.  In  the  absence  of  positive  data,  it  can 
only  be  asserted  that  the  above  dietary  stands  for  simplicity 
and  frugality.  Its  proteid-content  may  be  low,  but  the 
amount  of  proteid  taken  per  day  by  these  Highlanders  will 
obviously  depend  upon  the  quantity  of  food  consumed.  Oat- 
meal is  fairly  rich  in  proteid,  and  it  is  quite  conceivable  that 
the  amount  eaten  daily  may  be  such  as  to  result  in  a  high 
proteid  exchange. 

It  will  be  profitable  for  us  to  gain,  if  possible,  a  fairly  clear 
idea  of  the  quantities  of  food  requisite  for  our  average  man 
of  70  kilograms  body- weight ;  L  e.,  the  amounts  necessary  to 
provide  60  grams  of  proteid  and  2800  calories.  With  this 
end  in  view,  we  may  outline  a  simple  dietary,  expressed  in 
terms  that  will  convey  a  clear  impression,  showing  what  may 
be  eaten  without  overstepping  the  required  limits  of  proteid 
or  total  calories: 

BREAKFAST 

Proteid  Calories 

One  shredded  wheat  biscuit 3.15  grams      106 

30  grams 
One  teacup  of  cream       . 3.12  206 

120  grams 
One  German  water  roll 5.07  165 

57  grams 
Two  one-inch  cubes  of  butter       0.38  284 

38  grams 
Three-fourths  cup  of  coffee       0.26  ... 

100  grams 


PRACTICAL  APPLICATIONS  281 

BREAKFAST — continued. 

Proteid  Calories 

One-fourth  teacup  of  cream      .    .        . 0.78  51 

30  grams 
One  lump  of  sugar      38 

10  grams 

12776  850 

LUNCH 

Proteid  Calories 

One  teacup  homemade  chicken  soup     . 5.25  grams       60 

144  grams 
One  Parker-house  roll 3.38  110 

38  grams 
Two  one-inch  cubes  of  butter       0.38  284 

38  grams 
One  slice  lean  bacon 2.14  65 

10  grams 
One  small  baked  potato        1.53  55 

2  ounces,  60  grams 
One  rice  croquette 3.42  150 

90  grams 
Two  ounces  maple  syrup 166 

60  grams 

One  cup  of  tea  with  one  slice  lemon 

One  lump  of  sugar 38 

10  grams 

1616  928 


DINNER 

Proteid  Calories 

One  teacup  cream  of  corn  soup 3.25  72 

130  grams 
One  Parker-house  roll 3.38  110 

38  grams 
One-inch  cube  of  butter 0.19  142 

19  grams 
One  small  lamb  chop,  broiled 8.51  92 

lean  meat,  30  grams 
One  teacup  of  mashed  potato 3.34  175 

167  grams 
Apple-celery  lettuce  salad  with  mayonnaise  dressing      .     0.62  75 

50  grams 


282  THE  NUTRITION  OF  MAN 

DINNER  —  continued. 

Proteid  Calories 

One  Boston  cracker,  split 1.32  47 

2  inches  diameter,  12  grams 

One-half  inch  cube  American  cheese 3.35  60 

12  grams 

One-half  teacup  of  bread  pudding 6.25  160 

85  grams  t 

One  demi-tasse  coffee 

One  lump  of  sugar       38 

10  grams 

2O21  951 

The  grand  totals  for  the  day,  with  this  dietary,  amount  to 
58.07  grams  of  proteid  and  2729  calories.  It  is  of  course 
understood  that  these  figures  are  to  be  considered  as  only  ap- 
proximately correct,  but  the  illustration  will  suffice,  perhaps,  to 
give  a  clearer  understanding  of  the  actual  quantities  of  food 
involved  in  a  daily  ration  approaching  the  requirements  for  a 
man  of  70  kilograms  body- weight.  Further,  there  may  be 
suggested  by  the  figures  given  for  proteid  and  fuel  value  of 
the  different  quantities  of  foods,  a  clearer  conception  of  how 
much  given  dietary  articles  count  for  in  swelling  the  total 
values  of  a  day's  intake.  Moreover,  it  is  easy  to  see  how  the 
diet  can  be  added  to  or  modified  in  a  given  direction.  If  a 
little  more  proteid  is  desired  without  changing  materially  the 
fuel  value  of  the  food  a  boiled  egg  can  be  added  to  the  break- 
fast, for  example.  An  average-sized  egg  (of  58  grams)  con- 
tains 6.9  grams  of  proteid,  while  it  will  increase  the  fuel  value 
of  the  food  by  only  80  calories.  Or,  if  more  vegetable  proteid 
is  wished  for,  a  soup  of  split-peas  can  be  introduced,  without 
changing  in  any  degree  the  calorific  value  of  the  diet.  Thus, 
one  teacup  of  split-pea  soup  (144  grams)  contains  8.64  grams 
of  proteid,  while  the  fuel  value  of  this  quantity  may  be  only 
94  calories.  The  addition  of  one  banana  (160  grams)  will 
increase  fuel  value  153  calories,  but  will  add  only  2.28  grams 


PRACTICAL  APPLICATIONS  283 

of  proteid.  If  it  is  desired  to  increase  fuel  value  without 
change  in  the  pro teid-con tent  of  the  food,  recourse  can  always 
be  had  to  butter,  fat  of  meat,  additional  oil  in  salads,  or  to  syrup 
and  sugar. 

Such  a  menu  as  is  roughly  outlined,  however,  has  perhaps 
special  value  in  emphasizing  how  largely  the  proteid  intake 
is  increased  by  foods  other  than  meats,  and  which  are  not 
conspicuously  rich  in  proteid  matter.  All  wheat  products, 
for  example,  while  abounding  in  starch,  still  show  a  large  pro- 
portion of  proteid.  Thus,  shredded  wheat  biscuit  (1  ounce), 
which  is  a  type  of  many  kindred  wheat  preparations,  from 
bread  and  biscuit  to  the  various  so-called  breakfast  foods, 
yields  about  3  grams  of  proteid  per  ounce  and  approximately 
100  calories.  Even  potato,  which  is  conspicuously  a  carbohy- 
drate food  owing  to  its  large  content  of  starch,  yields  of 
nitrogen  the  equivalent  of  at  least  three-fourths  of  a  gram  of 
proteid  per  ounce.  If  larger  volume  is  desired  without  much 
increase  in  real  food  value,  there  are  always  available  green 
foods,  such  as  lettuce,  celery,  greens  of  various  sorts,  fruits, 
such  as  apples,  grapes,  oranges,  etc.  Too  great  reliance  on 
meats  as  a  type  of  concentrated  food,  on  the  other  hand, 
augments  largely  the  intake  of  proteid,  and  adds  a  relatively 
small  amount  to  the  fuel  value  of  the  day's  ration. 

An  ingenious  method  of  indicating  food  values,  which 
promises  to  be  of  service  in  sanatoria  and  under  other  condi- 
tions where  it  is  desirable  to  record  or  correct  the  diet  of  a 
large  number  of  persons,  has  been  devised  recently  by  Pro- 
fessor Fisher.1  The  method  aims  to  save  labor,  and  is  like- 
wise designed  to  visualize  the  magnitude  and  proportions  of 
the  diet.  The  food  is  measured  by  calories  instead  of  by 
weight,  a  "  standard  portion  "of  100  large  calories  being  the 
unit  made  use  of.  In  carrying  out  the  method,  foods  are 

1  Irving  Fisher:  A  new  method  for  indicating  food  values.  American 
Journal  of  Physiology,  vol.  15,  p.  417,  190G. 


284 


THE  NUTRITION   OF  MAN 


served  at  table  in  "  standard  portions,"  or  multiples  thereof. 
In  the  words  of  Fisher,  the  amount  of  milk  served,  for 
example,  "instead  of  being  a  whole  number  of  ounces, 
should  be  4.9  ounces  —  the  amount  that  contains  100  calories. 
This  'standard  portion'  constitutes  about  two-thirds  of  an 
ordinary  glass  of  milk.  Of  the  100  calories  which  it  con- 
tains 19  will  be  in  the  form  of  proteid,  52  in  fat,  and  29  in 
carbohydrate."  In  the  carrying  out  of  this  plan,  it  is  evident 
that  the  weight  of  any  food  yielding  100  calories  becomes 
a  measure  of  the  degree  of  concentration.  From  the  stand- 
point of  fuel  value,  olive  oil  is  probably  one  of  the  most 
concentrated  of  foods,  approximately  one-third  of  an  ounce 
containing  100  calories.  The  following  table,  taken  from 
Fisher's  description  of  his  method,  will  serve  to  show  the 
amounts  of  several  foods  constituting  a  "  standard  portion," 
and  also  the  number  of  calories  in  the  form  of  proteid,  fat, 
and  carbohydrate: 


Name  of  Food  and  "  Portion  " 
roughly  estimated. 

Weight  contain- 
ing 100  Calories. 

Proteid. 

Fat. 

Carbo- 
hydrate. 

Total. 

ounces 

grams 

calories 

calories 

calories 

calories 

053 

15 

130 

77.0 

10 

100 

Bananas,  one  large     .... 

3.50 

98 

5.0 

5.0 

90 

100 

Bread,  a  large  qlice    .... 

1.30 

37 

13.0 

6.0 

81 

100 

Butter,  an  ordinary  pat  .     .     . 

0.44 

13 

0.5 

99.5 

.. 

100 

Eggs,  one  large      

210 

60 

320 

68.0 

100 

680 

190 

49.0 

22.0 

29 

100 

Potatoes  one          

360 

100 

100 

1  0 

89 

100 

Whole  milk,  two-thirds  glass  . 

4.90 

140 

19.0 

52.0 

29 

100 

Beef  sirloin,  a  small  piece  .    . 

1.40 

40 

31.0 

69.0 

.. 

100 

Sugar,  five  teaspoons     .     .     . 

0.86 

24 

100 

100 

PKACTICAL  APPLICATIONS  285 

Obviously,  to  make  use  of  the  "  calories  per  cent "  method 
a  table  such  as  the  above,  covering  all  common  foodstuffs  and 
showing  the  weight  of  each  food  constituting  a  standard  por- 
tion, together  with  the  calories  of  proteid,  fat,  and  carbohy- 
drate in  this  portion,  is  necessary.  The  chief  advantage  of 
the  method,  however,  is  that  it  lends  itself  readily  to  geo- 
metrical representation  and  affords  an  easy  means  of  deter- 
mining the  constituents  of  combinations  of  different  foods  by 
use  of  a  simple  mechanism,  for  a  description  of  which  reference 
must  be  made  to  the  original  paper. 

Any  attempt  to  follow  a  daily  routine  which  accords  with 
the  true  needs  of  the  body  leads  necessarily  toward  foods 
derived  from  the  plant  kingdom,  with  the  adoption  of  simple 
dietary  habits,  and  with  greater  freedom  from  the  exciting  in- 
fluence of  the  richer  animal  foods.  There  is,  however,  virtue 
in  a  simple  dietary  that  appeals  and  satisfies,  and  in  so  doing 
testifies  to  the  completeness  with  which  it  meets  the  physi- 
ological requirements  of  the  body.  A  physician,1  writing  in 
the  "British  Medical  Journal,"  says :  "  I  determined  to  give  the 
minimum-of-proteid  diet  a  fair  trial  in  my  own  case.  The  re- 
sult was  that  I  was  relieved  of  a  life-long  tendency  to  acid 
dyspepsia  and  occasional  sick  headache ;  my  fitness  for  work, 
my  appetite  and  relish  for  food,  were  increased,  without  any 
diminution,  but  rather  a  slight  increase,  in  my  weight.  My 
practice  extends  over  a  wide  area  of  rough  mountainous 
country  involving  long  journeys  on  cycle,  on  foot,  driving, 
and  in  open  boats,  in  fair  and  foul  weather.  The  muscular 
exertion  and  endurance  necessary  for  the  work  would  seem  to 
require  a  large  proportion  of  proteid  and  a  generous  diet  alto- 
gether, but  since  I  began  to  experiment  I  have  suffered  less 
than  formerly  from  fatigue,  and  seem  to  eat  in  all  a  smaller 
quantity  of  food.  My  diet  consists  of : 


1  Aran  Coirce :  British  Medical  Journal,  April  7,  1906,  p.  829. 


286  THE  NUTRITION   OF  MAN 

Breakfast,  8.80  A.M.  —  Oatmeal  cakes,  bread  and  butter,  about  1  cubic  inch  of 
cheese  or  bloater  paste,  marmalade,  and  one  breakfast  cup  of  tea. 

Lunch,  1.30  P.M.  —  Same  as  breakfast,  with  occasionally  a  boiled  egg,  and 
sometimes  coffee  instead  of  tea. 

Dinner,  7  P.M.  —  Thick  soup  containing  vegetables,  with  bread,  followed  by 
suet  pudding  or  fruit  tart;  or  vegetable  stew,  containing  2  or  3  ounces  of  meat, 
with  boiled  potatoes,  followed  by  milk  pudding  and  jam,  and  occasionally  a 
cup  of  black  coffee." 

This  statement  of  personal  experience  is  in  close  accord 
with  statements  that  have  come  to  the  writer  in  hundreds  of 
letters  during  the  past  two  or  three  years,  from  persons  who 
have  for  some  reason  chosen  to  follow  a  more  abstemious 
mode  of  life.  Such  testimony  has  a  certain  measure  of  value 
in  that  it  offers  corroborative  evidence  of  the  beneficial  effects 
of  a  moderate  diet,  more  closely  in  accord  with  the  actual  de- 
mands of  the  body  for  food.  It  does  not,  however,  carry  quite 
that  degree  of  assurance  that  scientific  evidence,  gathered  by 
careful  observers  and  controlled  by  weights  and  measures  that 
hold  the  imagination  in  check,  affords  ;  and  so  we  may  turn  to  a 
different  type  of  testimony,  presented  in  an  elaborate  research 
by  Dr.  Neumann,1  of  the  Hygienic  Institute  at  Kiel,  an  experi- 
ment on  himself  extending  through  a  total  of  746  days. 

The  experiment  was  divided  into  three  periods.  In  the  first 
period  of  ten  months  the  subject,  with  a  body-weight  of  66.5 
kilograms,  consumed  daily  on  an  average  the  amounts  of  food 
indicated  in  the  following  table.  In  this  same  table  are  also 
included  the  daily  values,  based  on  the  preceding  data,  for  a 
body-weight  of  70  kilograms.  Thirdly,  the  table  likewise 
shows  the  amounts  of  utilizable  food  contained  in  the  food- 
stuffs actually  eaten,  on  the  basis  of  70  kilos  body-weight. 


1  Dr.  med.  et  phil.  R.  O.  Neumann  :  Experimentelle  Beitrage  zur  Lehre  von 
dem  taglichen  Nahrungsbedarf  des  Menschen  unter  besonderer  Beriicksichti- 
gung  der  notwendigen  Eiweissmenge.  Archiv  f iir  Hygiene,  Band  45,  p.  1, 1902. 


PEACTICAL  APPLICATIONS 


287 


AVERAGE  DAILY  FOOD  FOR  TEN  MONTHS 


Actually  consumed 
by  the  Subject, 
66.5  Kilos 

Calculated  for  a 
Body-weight  of 
70  Kilos 

Utilizable  Food 
for  a  Body-weight  of 
70  Kilos 

Proteid  .... 
Fat         ... 

66.1  grams 
83.5 

69.1  grams 
902 

57.3  grams 
812 

Carbohydrate 

230.0 

242.0 

225.0 

Alcohol  .... 

43.7 

45.6 

41.0 

Fuel  value  .    .    . 

2309  calories 

2427  calories 

2199  calories 

During  this  period  of  ten  months,  the  body- weight  of  the 
subject  remained  practically  constant,  or  indeed  showed  a 
slight  gain  up  to  67  kilograms.  All  the  functions  of  the 
body,  and  the  general  condition  of  good  health,  were  in  no 
wise  impaired ;  so  that  in  the  words  of  the  subject,  the  amount 
of  food  eaten  must  have  been  sufficient  for  the  needs  of  the 
body.  Somewhat  striking  is  the  fact  that  of  the  2309  calories 
in  the  daily  food,  more  than  one-fourth  was  derived  from  the 
beer  consumed  daily  (1200  c.c.).  Also  noticeable  is  the  rela- 
tively small  amount  of  carbohydrate  taken  daily,  only  about 
one-half  the  quantity  designated  by  Voit  as  the  average  re- 
quirement of  German  laborers.  Finally,  it  is  to  be  observed 
that  during  this  period  of  ten  months,  the  daily  consumption 
of  food  as  calculated  for  a  man  of  70  kilograms  body-weight, 
based  on  the  actual  food  consumption  of  the  subject  with  a 
weight  of  66.5  kilos,  was  not  widely  different  from  our  own 
statement  of  60  grams  of  proteid  and  2800  calories.  The 
tendency,  however,  in  Dr.  Neumann's  experiment  was  toward 
lower  fuel  values  and  somewhat  higher  proteid  consumption. 

In  a  second  period  of  50  days,  with  a  slightly  larger  daily 
intake,  Dr.  Neumann  observed  that  his  body  was  laying  by 
nitrogen,  i.  e.,  storing  up  proteid  on  a  daily  diet  of  76.5  grams 


288 


THE  NUTEITION  OF  MAN 


of  proteid  and  with  sufficient  fat  and  carbohydrate  to  furnish 
a  total  fuel  value  of  2658  calories.  In  the  final  period  of  8 
months,  the  following  data  were  obtained : 


AVERAGE  DAILY  FOOD  FOR  EIGHT  MONTHS 


Actually  consumed 
by  the  Subject, 
71.5  Kilos. 

Calculated  for  a 
Body-  Weight  of 
70  Kilos. 

Utilizable  Food  for  a 
Body-  Weight  of 
70  Kilos. 

Proteid      .    . 

76.2  grams 

74.0  grams 

61.4  grams 

Fat  .... 

109.0 

106.1 

95.5 

Carbohydrate 

168.9 

164.2 

152.7 

Alcohol     .    . 

5.5 

5.3 

4.7 

Fuel  value     . 

2057  calories 

1999  calories 

1766  calories 

During  this  period,  it  is  to  be  noted  that  the  fuel  value  of 
the  day's  food  averaged  only  2057  calories,  which  for  a  body- 
weight  of  70  kilograms  would  amount  to  less  than  2000  calo- 
ries. The  proteid  consumption,  however,  was  larger  than  we 
have  found  to  be  necessary  for  a  man  of  the  above  weight. 
Still,  the  facts  are  in  harmony  with  the  general  principle  that 
there  is  no  necessity  for  a  daily  intake  of  food  such  as  common 
usage  dictates,  there  being  obviously  a  wide  difference  between 
a  minimal  daily  consumption  of  118  grams  of  proteid  and 
3000  or  more  calories,  such  as  is  assumed  to  be  needed  by  a 
man  of  70  kilos,  and  74  grams  of  proteid  with  1999  calories. 
Under  the  latter  conditions,  the  subject  gained  a  kilogram  in 
weight  during  the  eight  months,  while  the  establishment  of 
nitrogen  equilibrium  testifies  to  the  now  generally  accepte^ 
view  that  it  is  quite  possible  for  the  body  to  establish  nitrogen 
equilibrium  at  different  levels,  i.e.,  with  different  quantities 
of  proteid  food  and  different  fuel  values. 

The  diet  made  use  of  by  Neumann  was  a  mixed  one,  con- 


PEACTICAL  APPLICATIONS 


289 


taining  a  great  variety  of  animal  and  vegetable  foods,  but 
withal  simple  and  moderate  in  quantity.  Calculated  per  kil- 
ogram of  body-weight,  the  average  consumption  of  food  ma- 
terial per  day  during  the  three  periods  was  as  indicated  in 
the  following  table : 


DAILY  FOOD  CONSUMPTION  PER  KILOGRAM  OF  WEIGHT 


Proteid. 

Fat. 

Carbohydrate. 

Alcohol. 

Calories 

First  Period     .     . 

grama 
0.99 

grams 

1.3 

grams 

34.5 

grams 

0.56 

34.7 

Second  Period     . 

1.10 

2.3 

33.4 

.    . 

59.7 

Third  Period  .    . 

1.00 

1.6 

23.4 

0.07 

28.5 

The  average  of  daily  food  consumption  for  the  total  of  746 
days  was  as  follows :  74.2  grams  proteid,  117  grams  fat,  213 
grams  carbohydrate,  and  2367  calories.  On  such  a  diet,  during 
this  long  period,  equilibrium  was  satisfactorily  maintained, 
thereby  furnishing  additional  evidence  that  quantities  of  food 
way  below  tho  so-called  normal  amounts  are  quite  adequate 
to  meet  the  needs  of  the  body.  There  is  no  conflict  whatever 
between  these  results  and  our  own  ;  they  both  point  in  the 
same  general  direction.  Perhaps  the  one  thing  that  needs  to 
be  again  emphasized,  however,  in  view  of  the  low  fuel  values 
used  by  Neumann,  is  that  while  they  proved  quite  adequate 
in  his  case,  the  demand  in  this  direction  is  governed  largely 
by  the  degree  of  bodily  activity.  In  fact,  Neumann's  results 
with  fuel  values  are  in  perfect  harmony  with  the  data  obtained 
by  us  with  professional  men,  but  the  writer  is  inclined  to 
believe  that  for  the  majority  of  mankind,  with  the  varying 
degrees  of  activity  and  muscular  exertion  called  for,  a  some- 
what larger  number  of  heat  units  is  desirable,  and  indeed  on 
many  occasions  demanded. 

Still,  it  is  perfectly  obvious  that  custom  has  greatly  exag- 

19 


290  THE  NUTRITION  OF  MAN 

gerated  the  fuel  values  required  in  ordinary  muscular  work, 
.and  such  results  as  are  here  presented  tend  to  emphasize  the 
true  relationship  between  actual  requirements  and  fuel  intake. 
Further,  it  must  not  be  overlooked  that  the  rate  of  proteid 
katabolism  is  governed  in  large  measure  by  the  amount  of 
non-nitrogenous  food,  and  consequently  a  too  narrow  margin 
in  the  consumption  of  the  latter  will  obviously  result  in  a 
higher  rate  of  proteid  exchange.  We  are  inclined  to  the 
belief  that  a  satisfactory  degree  of  bodily  efficiency  is  more 
liable  to  be  maintained  with  a  somewhat  larger  consumption 
of  carbohydrate  food,  combined  with  a  reduction  in  proteid 
food  to  a  level  nearer  our  own  figures.  It  will  be  observed 
that  the  average  amount  of  carbohydrate  taken  daily  by 
Neumann,  during  the  746  days,  was  only  213  grams,  while  the 
daily  consumption  of  fat  averaged  117  grams.  These  figures 
are  interesting  and  instructive  in  many  ways,  especially  as  in- 
dicating the  ease  with  which  the  body  accommodates  itself  to 
a  relatively  low  intake  of  proteid  food,  combined  with  a  small 
proportion  of  starches  and  sugars.  This  relationship  between 
carbohydrate  and  fat  might  well  occur  at  times  as  a  natural 
result  of  personal  taste,  but  as  a  general  rule  it  is  probably 
better,  from  the  standpoint  of  digestibility  and  general  availa- 
bility, for  the  daily  food  to  contain  a  larger  proportion  of 
carbohydrate. 

Under  this  head,  I  would  lay  special  stress  upon  the  value 
to  the  body  of  the  natural  sugars  as  well  as  of  starch.  We 
are  inclined  to  deprecate  the  widespread  use  of  candy,  especially 
among  children,  and  there  is  no  doubt  that  the  too  lavish  use 
of  sugar  in  such  concentrated  form  does  at  times  do  harm  ; 
but  when  eaten  as  an  integral  part  of  the  many  available  fruits 
its  use  cannot  be  too  highly  lauded,  for  both  young  and  old. 
Oranges,  grapes,  prunes,  dates,  plums,  and  bananas  are  espe- 
cially to  be  commended,  and  in  lesser  degree  peaches,  apricots, 
pears,  apples,  figs,  strawberries,  raspberries,  and  blueberries. 


PRACTICAL  APPLICATIONS  291 

In  all  of  these  fruits,  it  is  the  sugar  especially  that  gives  food 
value  to  the  article,  while  the  mild  acids  and  other  extrac- 
tives, together  with  the  water  of  the  fruit,  help  in  other  ways 
in  the  maintenance  of  good  health.  Where  personal  taste  and 
inclination  are  favorably  disposed,  the  first  six  fruits  named 
can  be  partaken  of  freely,  and  the  diet  of  the  young,  especially, 
can  be  advantageously  modified  by  the  liberal  use  of  such 
articles  of  food. 

Of  the  other  fruits,  apples  when  thoroughly  ripe  are 
above  reproach  if  properly  masticated,  but  the  raw  fruit  is 
somewhat  indigestible  when  swallowed  in  too  large  pieces,  and 
may  cause  trouble  to  a  delicate  stomach.  A  baked  apple,  on 
the  other  hand,  is  both  savory  and  wholesome,  and  if  served 
with  sugar  and  cream,  for  example,  constitutes  a  most  health- 
ful and  satisfying  article  of  food.  Peaches,  apricots,  and 
strawberries  as  ripe  fruits  are  likewise  exceedingly  valuable, 
but  here  personal  idiosyncrasy  frequently  comes  to  the  fore, 
especially  with  strawberries,  and  prohibits  their  free  use. 
The  peculiar  acidity  of  these  latter  fruits  is  occasionally  a 
source  of  trouble,  which  leads  to  their  avoidance  ;  but  this  is 
far  less  liable  to  happen  with  people  living  on  a  low  proteid 
diet  with  its  greater  freedom  from  purin  derivatives,  or  uric 
acid  antecedents.  Further,  there  is  a  tendency  on  the  part  of 
some  individuals  to  suffer  from  acid  fermentation  with  too 
liberal  use  of  starches  and  sugar,  but  as  a  rule  the  advantages 
of  ordinary  starchy  and  natural  sugar-containing  foods  cannot 
be  overestimated.  It  is  certainly  wise  to  give  them  a  con- 
spicuous place  in  the  daily  dietary  and  to  encourage  their  use, 
especially  by  children. 

As  has  been  stated  in  several  connections,  a  diet  which 
conforms  to  the  true  nutritive  requirements  of  the  body  must 
necessarily  lead  toward  vegetable  foods.  In  no  other  satisfac- 
tory way  can  excess  of  proteid  be  avoided,  and  at  the  same 
time  the  proper  calorific  value  be  obtained.  This,  however, 


292  THE  NUTRITION   OF  MAN 

does  not  mean  vegetarianism,  but  simply  a  greater  reliance 
upon  foods  from  the  plant  kingdom,  with  a  corresponding  dimi- 
nution in  the  typical  animal  foods.  This  raises  the  question 
of  the  possible  relation  of  diet  to  the  bacterial  processes  of 
the  intestine,  knowing,  as  we  do,  that  the  latter  are  of 
primary  importance  in  the  causation  of  certain  forms  of  auto- 
intoxication, etc.  Recent  studies  have  indicated  that  the  bac- 
terial flora  of  carnivorous  animals  is  quite  different  from  that 
of  herbivorous  animals,  and  this  being  so,  it  is  easy  to  see  how 
a  predominance  of  vegetable  or  animal  food  may  modify  the 
bacterial  conditions  of  the  intestinal  tract  in  man.  Dr. 
Herter1  has  reported  the  presence  in  the  intestines  of  cats, 
dogs,  tigers,  lion,  and  wolf  of  many  spore-holding  bacilli,  as 
well  as  free  spores  and  vegetative  forms  of  anaerobic  organ- 
isms ;  some  of  which  at  least  are  decidedly  pathogenic  when 
injected  into  the  subcutaneous  connective  tissue,  leading  to 
serious  and  even  fatal  results  within  twenty-four  hours. 
With  herbivorous  animals,  on  the  other  hand,  such  as  the 
buffalo,  goat,  horse,  elephant,  etc.,  the  predominating  organ- 
isms are  of  a  different  order  from  those  found  in  the  intes- 
tines of  the  carnivora;  proving  practically  non-pathogenic, 
or  only  slightly  so,  when  injected  subcutaneously,  and  less 
disposed  to  produce  putrefactive  changes  or  other  chemical 
decompositions. 

In  the  words  of  Dr.  Herter,  "  These  differences  in  the 
appearance  and  behavior  of  the  bacteria  derived  from  typ- 
ical carnivora  and  herbivora  suggest  that  the  habit  of  liv- 
ing upon  a  diet  consisting  exclusively  of  raw  meat  entails 
differences  in  the  types  of  bacteria  that  characterize  the  con- 
tents of  the  large  intestine.  The  occurrence  of  considerable 
numbers  of  spore-bearing  organisms  in  the  carnivora  points 
to  the  presence  of  anaerobic  putrefactive  forms  in  great  num- 

1  C.  A.  Herter :  Character  of  the  Bacterial  Flora  of  Carnivorous  and  Her- 
bivorous Animals.  Science,  December  28,  1906,  p.  859. 


PEACTICAL  APPLICATIONS  293 

bers.  The  results  of  subcutaneous  inoculations  into  guinea- 
pigs  bear  out  this  view  and  indicate  that  the  numbers  of 
organisms  capable  of  producing  a  hemorrhagic  oedema  with 
tissue  necrosis,  with  or  without  gas-production,  are  very  con- 
siderable. .  .  .  The  observations  recorded  are  of  much  in- 
terest in  relation  to  the  bacterial  processes  and  nutrition  of 
herbivorous  as  distinguished  from  carnivorous  animals,  and 
are  significant  furthermore  for  the  interpretation  of  bacterial 
conditions  found  in  man.  The  question  arises  whether  the 
abundant  use  of  meat  over  a  long  period  of  time  may  not 
favor  the  development  of  much  larger  numbers  of  spore- 
bearing  putrefactive  anserobes  in  the  intestinal  tract  than 
would  be  the  case  were  a  different  type  of  proteid  substituted 
for  meat."  While  it  may  be  said  truly  that  observations  of 
this  character  are  as  yet  not  sufficiently  numerous  or  conclu- 
sive to  warrant  positive  or  sweeping  statements,  yet  there  is 
a  suggestion  here  well  worthy  of  thoughtful  consideration  in 
its  general  bearing  on  the  nutrition  of  mankind. 

Simplicity  in  diet,  with  or  without  complete  abstinence 
from  meat,  is  often  resorted  to  as  a  means  of  relief  from  bodily 
ailments,  and  such  cases  sometimes  afford  striking  illustrations 
of  the  adequacy  and  benefits  of  a  relatively  low  intake  of  food. 
Cases  of  this  sort,  perhaps,  are  more  frequently  observed 
among  elderly  people,  where  the  daily  requirements  are  not  so 
great  as  with  younger  and  more  active  persons,  -but  they  offer 
evidence  in  support  of  our  main  thesis  that  dietary  habits  are 
no  guarantee  of  bodily  requirements.  I  have  in  mind  the  de- 
tails of  an  exceedingly  interesting  case  reported  with  much 
care  by  Dr.  Fenger ; l  the  case  of  a  man  who  at  61  years  of 
age,  after  a  long  period  of  poor  health,  brought  himself 
quickly  into  a  condition  of  sound  health  by  a  daily  diet  char- 
acterized by  extreme  simplicity  and  with  an  exceedingly  low 

1  Dr.  S.  Fenger :  Beitrage  zur  Kenntniss  des  Stoffwechsels  im  Greisenalter. 
Skandinavisches  Archiv  fur  Physiologic,  Band  16,  p.  222,  1904. 


294  THE    NUTRITION   OF  MAN 

fuel  value.  The  daily  diet  made  use  of  during  the  fifteen 
years  the  subject  was  under  examination  consisted  of  the 
following  articles : 

1889-1892 :  1  egg,  1  quart  of  oatmeal  soup,  2  quarts  of  skim  milk,  1£  ounces  of 
red  wine,  £  ounce  of  sugar. 

1892-1894 :  2  eggs,  1  quart  of  oatmeal  soup,  2  quarts  of  skim  milk,  1|  ounces 
of  red  wine,  \  ounce  of  sugar. 

1894-1900:  3  eggs,  1  pint  of  oatmeal  soup,  2  quarts  of  skim  milk,  1|  ounces  of 
red  wine,  £  ounce  of  sugar,  2  ounces  of  plum  and  raspberry  juice. 

1900-1903 :  3  eggs,  1  pint  of  barley  soup,  3  pints  of  sweet  milk,  1  pint  of  butter- 
milk, \\  ounces  of  red  wine,  £  ounce  of  sugar,  2  ounces  of  plum  and 
raspberry  juice. 

It  will  be  observed  that  during  these  fifteen  years  the  sub- 
ject partook  of  no  meat  whatever,  and  further,  that  the  diet 
was  wholly  in  fluid  form.  At  the  close  of  this  long  period, 
the  subject,  being  then  75  years  of  age,  was  reported  as  well 
and  in  good  health,  with  satisfactory  physical  condition  for  a 
person  of  his  years.  He  was  a  man  of  small  body-weight, 
only  42  kilograms,  but  during  this  period  of  voluntary  re- 
striction in  diet,  he  suffered  no  loss.  It  is  perhaps  worthy  of 
comment  also  that  all  through  this  lengthy  period  no  salt  was 
taken  other  than  what  was  naturally  present  in  the  simple 
foods  made  use  of.  The  point  to  attract  our  attention  espe- 
cially, however,  is  that  for  fifteen  years,  during  which  the 
quality  and  quantity  of  this  man's  food  was  carefully  observed, 
body-weight,  general  good  health,  and  physical  vigor  were  all 
maintained,  together  with  freedom  from  the  ills  of  previous 
years  and  with  a  daily  diet  characterized  by  extreme  simplicity. 
The  chemical  composition  of  the  diet  was  likewise  peculiar, 
particularly  in  its  exceedingly  low  fuel  value.  The  following 
table  shows  the  amounts  of  proteid,  fat,  and  carbohydrate 
consumed  daily  during  the  four  periods  designated : 


PRACTICAL  APPLICATIONS 


295 


Period. 

Proteid. 

Fat. 

Carbo- 
hydrate. 

Calories. 

Calories 
per  Kilo- 
gram. 

1  Proteid 
per  Kilo- 
gram. 

1889-1892 

grams 

79.8 

grams 
21.7 

grams 
152.0 

1126 

26 

grams 
1.90 

1892-1894 

85.2 

27.0 

152.0 

1200 

28 

2.03 

1894-1900 

87.0 

30.1 

150.1 

1230 

29 

2.07 

1900-1903 

84.4 

73.7 

148.3 

1600 

38 

2.00 

Especially  noticeable  here  is  the  low  intake  of  fat  and  car- 
bohydrate, with  the  corresponding  low  fuel  value,  and  also  the 
relatively  high  consumption  of  proteid,  averaging  2.0  grams 
daily  per  kilogram  of  body-weight.  Dr.  Fenger  concludes 
that  for  a  man  of  this  age  and  weight,  with  the  relative  inac- 
tivity characteristic  of  old  age,  a  heat  value  in  the  intake  of  30 
calories  per  kilogram  of  body-weight  is  quite  sufficient  for  the 
needs  of  the  body.  This  may  be  quite  true,  but  to  maintain 
nitrogen  equilibrium  under  such  conditions  requires  a  larger 
intake  of  proteid  food  than  is  desirable.  It  will  be  observed 
that  in  the  last  period  of  four  years  a  very  decided  change  in 
the  diet  was  instituted ;  proteid  was  diminished  somewhat, 
but  the  noticeable  change  was  the  decided  increase  in  fat,  pro- 
duced in  large  measure  by  the  substitution  of  whole  milk, 
with  its  contained  cream,  for  skim  milk.  In  the  words  of  Dr. 
Fenger,  this  change  was  necessitated  by  the  appearance"  of 
gout  in  the  subject.  From  superficial  examination  of  the  die- 
tary of  the  preceding  eleven  years  there  would  seem  no  occa- 
sion for  criticising  the  subject  for  high  living,  and  yet  I 
believe  we  are  quite  within  the  limits  of  reason  in  saying  that 
the  proteid  exchange  for  a  subject  of  this  body-weight  was 
altogether  too  high.  The  heat  requirements  of  the  body  were 
being  met  in  an  unnecessarily  large  degree  from  the  breaking 
down  of  proteid  material,  with  consequent  formation  of  exces- 


296  THE  NUTRITION  OF  MAN 

sive  nitrogenous  waste,  among  which  uric  acid  was  plainly 
conspicuous. 

One  comment  to  be  made  here  is  that  meat  and  other  rich 
purin-containing  foodstuffs  are  not  the  only  source  of  gout 
and  uric  acid.  Excessive  proteid  katabolism,  both  exogenous 
and  endogenous,  is  a  possible  source  of  danger  in  this 
respect,  and  the  above  subject,  though  living  on  an  ex- 
ceptionally simple  diet,  was  consuming  far  more  proteid  per 
kilogram  of  body-weight  than  was  necessary  or  desirable. 
Increase  of  fatty  food  naturally  served  to  diminish  the  rate  of 
proteid  katabolism,  and  this  could  have  been  advantageously 
accompanied  by  a  still  greater  reduction  in  the  amount  of 
proteid  ingested,  and  a  larger  addition  of  non-nitrogenous  food- 
stuffs. In  old  age,  there  is  naturally  a  slowing  down  of  the 
metabolic  processes,  and  both  nitrogen  equilibrium  and  body 
equilibrium  can  be  satisfactorily  maintained  by  a  relatively 
small  intake  of  food  and  with  gain  to  the  body  ;  but  there  is 
every  reason  to  believe  that  economy  in  proteid  food  can  be 
more  advantageously  adopted  than  economy  in  non-nitroge- 
nous foodstuffs. 

Finally,  we  may  call  attention  to  the  many  possibilities  of 
an  intelligent  modification  of  the  daily  diet  to  the  temporary 
needs  of  the  individual.  The  season  of  the  year,  summer  and 
winter,  the  climate,  the  degree  of  activity  of  the  body,  the 
state  of  health,  temporary  ailments,  etc.,  all  present  special 
conditions  which  admit  of  particular  dietetic  treatment.  In 
hot  summer  weather,  for  example,  there  is  plainly  less  need 
for  food  than  in  the  cold  winter  season,  especially  for  fat  with 
its  high  calorific  value.  During  the  cold  part  of  the  year,  the 
lower  temperature  of  the  surrounding  air,  with  the  tendency 
toward  greater  muscular  activity,  calls  for  more  extensive 
chemical  decomposition  in  order  to  meet  the  demand  for 
heat,  and  the  energy  of  muscular  contraction.  There  is  per- 
haps no  special  reason  for  any  material  change  in  the  amount 


PRACTICAL  APPLICATIONS  297 

of  proteid  food  consumed  in  the  two  seasons,  except  in  so  far 
as  it  may  seem  desirable  at  times  to  take  advantage  of  the 
well-known  stimulating  properties  of  proteid  to  whip  up 
the  general  metabolism  of  the  body,  in  harmony  with  the 
principle  that  all  metabolic  processes  may  need  spurring  to 
meet  the  demands  of  a  greatly  lowered  temperature  in  the 
surrounding  air. 

Fuel  value,  however,  should  be  increased  somewhat  dur- 
ing the  winter  months  in  our  climate.  Fat  promises  the  larg- 
est amount  of  energy,  but  there  is  more  of  a  tendency  to 
store  up  excess  of  fat  than  of  carbohydrate,  hence  the  latter 
foods  have  certain  advantages  as  a  source  of  the  additional 
energy  needed  during  cold  weather.  In  warm  weather,  it 
should  be  our  aim  to  diminish  unnecessary  heat  production  as 
much  as  possible,  though  it  must  be  remembered  that  the 
body  is  to  be  maintained  approximately  at  least  in  equilibrium, 
and  this  calls  for  an  adequate  amount  of  food.  Lighter  foods, 
however,  may  be  advantageously  employed,  such  as  fruits, 
vegetables,  fresh  fish,  etc.  Fats  and  fat  meats  especially  are 
to  be  avoided,  not  only  because  there  is  no  specific  need  for 
them,  but  particularly  on  account  of  a  greater  sensitiveness  of 
the  gastro-intestinal  tract  during  the  hot  seasons  of  the  year, 
that  is  liable  to  result  in  a  disturbance  whenever  undue  quan- 
tity of  rich  or  heavy  food  is  taken.  Further,  in  hot  summer 
weather  we  may  advantageously  live  more  largely  on  foods 
served  cold,  and  thereby  avoid  the  heat  ordinarily  introduced 
into  the  body  by  hot  fluids  and  solids.  These,  however,  are 
all  obvious  physiological  truths,  constituting  a  form  of  physio- 
logical good  sense  the  application  of  which  calls  for  no  special 
expert  knowledge. 

Less  obvious,  though  no  less  important,  is  the  partial  pro- 
tection that  can  be  afforded  to  weakened  or  disabled  kidneys 
by  judgment  and  discrimination  in  the  matter  of  diet.  In 
acute  or  chronic  nephritis,  forms  of  so-called  B right's  disease, 


THE  NUTRITION  OF  MAN 

.iS  there  not  danger  of  overtaxing  organs  already  weakened  by 
placing  upon  them  the  daily  duty  of  excreting  large  amounts 
of  solid  nitrogenous  waste,  as  well  as  of  the  various  inorganic 
salts  which  are  so  intimately  associated  with  many  of  the 
organic  foodstuffs?  The  consumption  of  excessive  and  un- 
necessary amounts  of  proteid  food  simply  means  the  ultimate 
formation  of  just  so  much  more  urea,  uric  acid,  etc.,  which 
must  be  passed  out  through  the  kidneys.  In  the  words  of 
Bunge,  "  There  is  no  organ  in  our  body  so  mercilessly  ill 
treated  as  the  kidneys.  The  stomach  reacts  against  overload- 
ing. The  kidneys  are  obliged  to  let  everything  pass  through 
them,  and  the  harm  done  to  them  is  not  felt  till  it  is  too  late 
to  avoid  the  evil  consequences."  It  would  seem  the  part  of 
wisdom,  therefore,  to  adjust  the  daily  intake  of  proteid  food  to 
as  low  a  level  as  is  consistent  with  the  true  needs  of  the  body, 
in  those  cases  where  the  kidneys  are  at  all  enfeebled,  or  where 
it  seems  desirable  to  exercise  due  precaution  as  a  possible 
means  of  prevention. 

Equal  care  is  frequently  called  for  in  connection  with  the 
mineral  matters  which  enter  so  largely  into  many  natural 
foodstuffs,  or  which  are  introduced  as  condiments.  As  an 
illustration,  we  may  note  one  or  two  peculiarities  in  the  dis- 
tribution of  sodium  and  potassium  salts  in  the  tissues  of  the 
body.  Potassium  is  an  indispensable  constituent  of  every  liv- 
ing cell,  and  the  latter  has  the  power  of  absorbing  and  holding 
on  to  such  amounts  of  this  particular  element  as  may  be  nec- 
essary for  the  functional  activity  of  the  tissue  of  which  it  is 
a  part.  Sodium,  on  the  other  hand,  stands  in  a  different 
relationship  to  living  structures.  It  is  widely  distributed, 
but  in  the  higher  animals,  as  in  man,  sodium  salts  are  most 
abundant  in  the  fluids  of  the  body,  notably  in  the  plasma 
of  the  blood.  Herbivorous  animals  have  a  strong  liking 
for  sodium  chloride  or  common  salt,  but  this  is  not  true  of 
carnivorous  animals  ;  indeed,  the  latter  animals  have  a  great 


PRACTICAL  APPLICATIONS  299 

dislike  for  salty  articles  of  food.  Vegetable  products  are 
all  rich  in  potassium  salts,  whereas  ordinary  animal  foods, 
such  as  meat,  eggs,  milk,  and  blood,  are  relatively  poor  in  this 
element. 

It  is  claimed  that  the  abundance  of  potassium  salts  in 
vegetable  foods  is  the  cause  of  the  apparent  need  for  so- 
dium chloride  by  herbivorous  animals,  and  in  lesser  degree  by 
man.  This  is  explained  by  supposing  that  when  the  salts  of 
potassium  reach  the  blood  by  absorption  of  the  vegetable 
foods,  an  interchange  takes  place  with  the  sodium  chloride  of 
the  blood  plasma.  "  Chloride  of  potassium  and  the  sodium 
salt  of  the  acid  which  was  combined  with  the  potassium  are 
formed.  Instead  of  the  chloride  of  sodium,  therefore,  the 
blood  now  contains  another  sodium  salt,  which  did  not  form 
part  of  the  normal  composition  of  the  blood,  or  at  any  rate 
not  in  so  large  a  proportion.  A  foreign  constituent  or  an 
excess  of  a  normal  constituent,  i.  e.,  sodium  carbonate,  has 
arisen  in  the  blood.  But  the  kidneys  possess  the  function  of 
maintaining  the  same  composition  of  the  blood,  and  of  thus 
eliminating  every  abnormal  constituent  and  any  excess  of  a 
normal  constituent.  The  sodium  salt  formed  is  therefore 
ejected  by  the  kidneys,  together  with  the  chloride  of  potas- 
sium, and  the  blood  becomes  poorer  in  chlorine  and  sodium. 
Common  salt  is  therefore  withdrawn  from  the  organism  by 
the  ingestion  of  potassium  salts.  This  loss  can  only  be  made 
up  from  without,  and  this  explains  the  fact  that  animals  which 
live  on  a  diet  rich  in  potassium,  have  a  longing  for  salt" 
(Bunge).  It  is  certainly  a  fact  worthy  of  note  that  man  takes 
only  one  salt  as  such  in  addition  to  those  that  are  naturally 
present  in  his  food,  and  it  is  equally  significant  that  sodium 
chloride  is  by  no  means  lacking  in  ordinary  foodstuffs.  If 
the  individual  lives  entirely  on  animal  foods,  he  has  no  desire 
for  salt,  but  as  soon  as  he  adopts  a  vegetable  diet  the  craving 
for  salt  shows  itself.  Vegetable  foods,  however,  are  not  all 


300  THE  NUTBITION   OF  MAN 

alike  in  their  content  of  potassium  salts;  some,  like  rice, 
contain  relatively  little,  while  others,  like  potatoes,  peas,  and 
beans,  are  comparatively  rich  in  this  element. 

We  may  recognize  in  these  statements  a  physiological  de- 
mand for  a  certain  amount  of  salt,  especially  when  vegetable 
foods  enter  into  the  daily  dietary,  but  there  is  no  justification 
for  the  employment  of  such  quantities  as  are  generally  made 
use  of.  Where  the  vegetable  food  is  largely  rice,  a  small 
fraction  of  a  gram  of  salt  is  really  sufficient  for  all  physiolog- 
ical purposes  ;  and  in  those  cases  where  ordinary  cereals,  leg- 
umes, potatoes,  etc.,  constitute  the  chief  part  of  the  dietary, 
a  few  grams  of  salt,  at  the  most,  will  suffice  to  meet  the  daily 
needs.  Common  usage,  however,  frequently  raises  the  amount 
consumed  to  25  grams  or  more  per  day,  the  bulk  of  which  is  at 
once  eliminated  through  the  kidneys ;  thereby  entailing  a  cer- 
tain amount  of  renal  activity,  which  must,  it  would  seem, 
constitute  something  of  a  strain  upon  organs  ordinarily  hard 
worked  at  the  best.  "Do  we  not  impose  too  great  a  task 
upon  them,  and  may  it  not  be  fraught  with  serious  conse- 
quences ?  When  on  a  diet  of  meat  and  bread,  without  salt, 
we  excrete  not  more  than  from  6  to  8  grams  of  alkaline  salts 
in  twenty-four  hours.  With  a  diet  of  potatoes,  and  a  corre- 
sponding addition  of  salt,  over  100  grams  of  alkaline  salts  pass 
through  the  kidneys  in  the  day.  May  not  there  be  danger 
in  this?  The  habit  of  drinking  spirituous  liquors,  which 
moreover  is  reckoned  one  of  the  causes  of  chronic  nephritis, 
also  brings  about  the  immoderate  use  of  salt,  and  thus  one 
sin  against  nature  leads  to  another  "  (Bunge). 

The  moral  we  would  draw  (from  these  observations)  is  that 
in  weakened  conditions  of  the  kidneys  there  is  reason  in  reduc- 
ing the  rate  of  proteid  exchange  to  the  lowest  level  consis- 
tent with  the  maintenance  of  equilibrium  and  the  preservation 
of  strength  and  vigor,  thereby  diminishing  the  amount  of  ni- 
trogenous waste  to  be  eliminated  and  the  consequent  strain 


PRACTICAL  APPLICATIONS  301 

upon  these  organs.  Further,  there  is  suggested  moderation 
in  the  amount  of  salt  to  be  used  daily,  and  some  circumspec- 
tion in  the  amount  and  quality  of  vegetable  foods  consumed 
in  order  to  regulate  more  effectually  the  quantity  of  saline 
waste  to  be  handled  by  the  kidneys.  These  conclusions  are 
just  as  worthy  of  consideration  as  the  more  obvious  rule  that 
in  diabetes  or  glycosuria  proper  precaution  must  be  observed 
in  the  eating  of  carbohydrate  foods.  In  gout  and  rheumatism, 
accumulated  physiological  knowledge  teaches  plainly  the 
necessity  of  avoiding  those  foods  that  are  rich  in  purin-con- 
taining  compounds.  Uric  acid  owes  its  origin  in  part  at 
least  to  substances  of  this  class ;  and  as  an  ounce  of  prevention 
is  worth  more  than  a  pound  of  cure,  we  may  by  proper  mod- 
eration in  the  use  of  such  foods  save  ourselves  from  the  dis- 
agreeable effects  of  accumulated  uric  acid  deposits. 

In  conclusion,  the  nutrition  of  man,  if  it  is  to  be  carried 
out  by  the  individual  in  a  manner  adapted  to  obtaining  the 
best  results,  involves  an  intelligent  appreciation  of  the  needs 
of  the  body  under  different  conditions  of  life,  and  a  willing- 
ness to  accept  and  put  in  practice  the  principles  that  scientific 
research  has  brought  to  light,  even  though  such  principles 
stand  opposed  to  old-time  traditions  and  customs.  The  master 
words  which  promise  help  in  the  carrying  out  of  an  intelligent 
plan  of  living  are  moderation  and  simplicity ;  moderation  in 
the  amount  of  food  consumed  daily,  simplicity  in  the  character 
of  the  dietary,  in  harmony  with  the  old  saying  that  man  eats 
to  live  and  not  lives  to  eat.  In  so  doing  there  is  promise  of 
health,  strength,  and  longevity,  with  increased  efficiency,  as 
the  reward  of  obedience  to  Nature's  laws. 


INDEX 

A- 

Abderhalden,  Emil,  35 

Absorption,  a  physiological  process,  41 

diffusion  as  a  factor  in,  41 

from  the  stomach,  31 

in  intestine,  37 

of  fats,  43,  49 

of  fats,  in  dogs  on  low  proteid  diet,  233,  261 

of  food  products,  by  blood,  44 

of  peptones,  41 

of  proteid  in  dogs  on  low  proteid  diet,  233,  262 

of  proteid  products,  47 

of  proteoses,  41 

osmosis,  as  factor  in,  41 

paths  of,  44 

reconstruction  of  proteid  during,  42 

selective  action,  of  sugars,  47 
Acid,  aspartic,  34,  67,  259 
glutaminic,  34,  259 
hydrochloric,  25,  26 
uric,  73 

uric,  excretion  of,  as  influenced  by  diet,  144 
Acids,  amino,  34 

diamino,  34 
Adenase,  71 
Adenin,  72 
Aldehydase,  64 
Amino  acids,  34,  67 
Ammonia,  70,  259 
Amylopsin,  32 
Anabolism,  50 

Animals,  influence  of  low  proteid  diet  on  high  proteid,  231,  233,  243 
Animal  starch,  see  Glycogen 
Appetite,  in  relation  to  food  requirements,  162 
Arginin,  34,  68,  70,  259 
Argutinsky,  views  on  muscle  work,  123 
Aspartic  acid,  34,  67,  259 
Assimilation  limits  of  sugars,  47 
Athlete,  photograph  of,  190 

Athletes,  fuel  value  of  food  of,  on  low  proteid  diet,  198 
strength  tests  of,  on  low  proteid  diet,  206 


304  INDEX 

Athletes,  true  proteid  requirement  of,  186 
Atwater  and  Benedict,  109,  111 
Autodigestion  (see  Autolysis),  63 
Autolysis,  12 
Availability,  of  foods,  12 

of  carbohydrates,  as  source  of  energy,  45 


B 

Bacterial  flora  in  intestine,  of  carnivora,  292 
of  herbivora,  292 

Bacterial  processes  in  intestine,  in  relation  to  food,  292 
Balance,  nutritive,  as  affected  by  various  factors,  117,  118 
Basal  energy  exchange,  104 

Beaumont,  William,  on  movements  of  stomach,  27 
Benedict,  F.  G.,  see  Atwater  and  Benedict 
Bergell  and  Lewin,  36 
Beriberi,  and  diet,  224 
Blood,  absorption  of  food  products  by,  44 

behavior  of  disaccharides  when  introduced  into,  39 

effects  of  injection  of  proteoses  and  peptones  into,  41 

relation  of  sugar  in,  to  glycogen,  46 

sugar  in,  45 
Body,  amounts  of  food  required  to  furnish  proteid  needs  of,  274 

efficiency  of,  as  a  machine,  111 

equilibrium,  78 

nature  of  oxidation  in  the,  60 

needs  of  nitrogen  by,  4 

needs  for  food  by,  169 

needs  and  dietary  habits,  268 

needs  of  proteid  by,  268,  272 

relation  of  oxygen  to  decompositions  in,  61 

resistance,  see  Resistance 

sample  dietary  supplying  needs  of,  280 

site  of  oxidation  in,  62 

surface,  relation  to  energy  exchange,  104,  105 

surface,  relation  to  nitrogen  requirement  in  dogs,  248 
Body- weight,  on  low  proteid  diet,  175,  181,  185,  190,  199,  245-255 

relation  to  proteid  requirement,  184,  188,  198,  227 
Bright's  disease,  see  Nephritis 

Breisacher,  L.,  on  minimum  proteid  requirement,  172 
Bunge,  124 

C 

Calorie,  14 

Calorimeter,  respiration,  102 

Cane  sugar,  assimilation  limit  of,  47 

behavior  when  introduced  into  blood,  39 

utilization  of,  40 
Cannon,  W.  B.,  on  muscular  movements  of  stomach,  28,  29 


INDEX  305 

Carbon  dioxide,  output  in  rest,  111,  112 

dioxide,  output  during  work,  111,  123 
equilibrium,  84 
excretion,  during  fasting,  84 
moiety  of  proteid,  129 

Garni vora,  bacterial  flora  in  intestine  of,  292 
Carbohydrates,  as  food,  6 

as  fuel,  6 

as  heat  producers,  58 

as  proteid  sparers,  92 

as  source  of  energy,  128 

as  source  of  energy  in  fasting,  81 

as  source  of  energy  in  work,  58 

availability  of,  13 

availability  of,  as  source  of  energy,  45 

composition  of,  5 

formation  from  proteid,  129 

fuel  value  of,  15 

in  foodstuffs,  7 

liver  as  regulator  of,  45 

respiratory  quotient  of,  107 
Casein,  cleavage  products  of,  70 

Caspari  and  Glassner,  on  minimum  proteid  requirement  in  man,  172 
Cellulose,  in  vegetables,  influence  on  digestion,  263 
Chemical  character  of  proteid,  influence  on  nutrition,  256 

composition  of  foodstuffs,  7 
Circulating  proteid,  134 

Clapp,  S.  H.  (see  Osborne  and  Clapp,  on  proteid  cleavage  products),  258 
Cleavage,  oxidative,  61 
Climbing,  oxygen  consumption  in,  116 
Cogan,  Thomas,  on  temperance  in  food,  166 
Cohnheim,  Otto,  on  proteid  decomposition,  36 
Composition,  of  proteid,  3 

of  carbohydrate,  5 
of  fat,  6 

Cornaro,  Louis,  on  temperance  in  food,  168 
Cost  of  foods  in  relation  to  nutritive  value,  277 
Creatin,  74 
Creatinin,  74 

excretion,  as  influenced  by  diet,  144 
Curtis,  Edward,  Nature  and  Health,  2,  5,  214 


Dapper,  Max,  99 
Dangers  of  underfeeding,  214 
Degeneration,  fatty,  270 
Deuteroproteose,  67,  69 
Dextrins,  21,  37 
Dextrose,  37 

20 


306  INDEX 

Dextrose,  assimilation,  limit  of,  47 

utilization  of,  40 
Diabetes,  phloridzin,  130 
Diamino  acids,  34 
Diet,  and  beriberi,  224 

and  renal  activity,  297 

effects  of  exclusive  proteid,  upon  rats,  239 

effects  of  intemperance  in,  270 

effects  of  rice,  on  rats,  240 

fat  absorption  in  dogs  on  low  proteid,  233,  261 

influence  of,  on  creatin  in  excretion,  144 

exclusive  proteid,  on  progeny  in  rats,  240 
on  growth  in  rats,  239 
monotony  in,  242 

on  oxygen  consumption  in  man  at  rest,  126 
on  oxygen  consumption  in  man  at  work,  126 
on  respiratory  quotient  in  man  at  rest,  126 
on  respiratory  quotient  in  man  at  work,  126 
rice,  on  growth  in  rats,  240 
on  urea  excretion,  144 
on  uric  acid  excretion,  144 
vegetable,  upon  dogs,  254,  256 
in  relation  to  nephritis,  297 
in  relation  to  nitrogen  distribution  in  urine,  144 
in  relation  to  seasons  of  the  year,  296 
of  Highlanders,  279 
low  proteid,  influence  on  body- weight  in  dogs,  245,  249,  250,  251,  252, 

255 

nitrogen  excretion  during  severe  work  on  exclusive  proteid,  123,  124 
philosophy  of  a  mixed,  92,  276 
relation  of  endurance  to  low  proteid,  210,  212 
relation  of  inorganic  salts  to,  299,  300 
relation  of  work  to,  126 
relation  of  vegetable  food  to  low  proteid,  291 
sample,  of  soldiers,  194 
sample,  in  experiments  on  true  proteid  requirement  in  man,  178,  182, 

189,  195 

simplicity  in,  advantages  of,  279,  293 
temperance  in,  270 

utilization  of  fat  in  dogs  on  low  proteid,  261 
utilization  of  nitrogen  in  dogs  on  low  proteid,  262 
variety  in,  229,  242 
Diets,  normal,  see  Standard  diets 

standard,  155 

Dietary  habits,  in  relation  to  needs  of  body,  268 
of  fruitarians,  215 
of  Japanese,  225 

sample,  supplying  needs  of  body,  280 
standards,  use  of  the  term,  272 
Dietetic  customs  of  mankind,  154 


INDEX  307 

Dietetics,  habit  in,  159 
Diffusion,  as  factor  in  absorption,  41 
Digestibility,  see  Availability 
Digestion,  gastric,  of  proteids,  26 

importance  of  gastric,  30 
influence  of  cellulose  in  vegetables  on,  263 
in  the  stomach,  25 
object  of  gastric,  30 
of  fat,  in  intestine,  36 
of  fat,  in  stomach,  36 
of  starch,  21 

products  of  pancreatic,  of  fats,  36 
products  of  pancreatic,  of  proteids,  34,  67 
products  of  pancreatic,  of  starch,  37 
products  of  salivary,  21 
salivary,  in  stomach,  23 

Digestive  products,  reconstruction  of  proteid  from,  42 
Disease,  relation  of  excessive  proteid  consumption  to,  269 
Dogs,  effects  of  low  proteid  diet  on,  232-236,  245-255 
fasting  experiments  on,  82 
fat  absorption  in,  on  low  proteid  diet,  233,  261 
fuel  value  requirement  of,  234,  236,  245-255 
influence  of  low  proteid  diet  upon  body- weight  in,  245-255 
influence  of  vegetable  diet  on,  254,  256 
nitrogen  requirement  of,  234,  235,  236,  245-255 
photographs  of ,  248 

proteid  absorption  in,  on  low  proteid  diet,  233,  262 
proteid  requirement,  experiments  by  Munk,  232 
proteid  requirement,  experiments  by  Rosenheim,  234 
proteid  requirement,  experiments  by  Jagerroos,  236 
proteid  requirement,  experiments  by  author,  243 
utilization  of  fat  in,  on  low  proteid  diet,  261 
utilization  of  nitrogen  in,  on  low  proteid  diet,  262 
Disaccharides,  utilization  of,  40 


E 

Edestin,  cleavage  products  of,  70 

Efficiency  of  body,  as  a  machine,  111 

Egg  albumin,  cleavage  products  of,  70 

Endogenous  metabolism,  145,  146 

Endurance,  relation  of,  to  low  proteid  diet,  210,  212 

Energy,  availability  of  carbohydrates,  as  source  of,  45 

basal  exchange,  104 

carbohydrate  as  source  of,  128 

carbohydrate  as  source  of,  in  fasting,  81 

conservation  of,  in  man,  103 

exchange,  effect  of  muscular  work,  109,  110,  113,  11. 

exchange,  factors  modifying,  105,  106 


308  INDEX 

Energy,  exchange,  in  relation  to  work,  119 

exchange  proportional  to  body  surface,  104,  105 
fat  as  source  of,  128 
fat  as  source  of,  in  fasting  81 
foods  as  source  of,  15 
metabolism  of,  in  man,  103 
of  muscle  contraction,  121 
origin  of,  in  fasting,  81 
output,  in  man,  103 
produced  by  man,  106 
proteid  as  source  of,  122,  123,  124,  129 
proteid  as  source  of,  in  fasting,  81 
source  of,  in  body,  21,  121 
source  of,  during  fasting,  in  work,  125 
Enterokinase,  33 
Enzymes,  deamidizing,  71,  72 
in  gastric  juice,  25 
in  pancreatic  juice,  32 
in  saliva,  20 

intracellular,  63,  71,  72,  75 
reversible  action  of,  21 
specificity  of,  21 
Equilibrium,  carbon,  84 

nitrogenous,  78 
of  body,  78 
Erepsin,  34 
Exchange,  basal  energy,  104 

of  energy,  as  affected  by  work,  109,  110,  113,  115,  119 
of  energy,  factors  modifying,  105,  106 
of  energy,  relation  to  body  surface,  104,  105 
Exogenous  metabolism,  145,  146 


Fasting,  carbohydrates  as  source  of  energy  in,  81 

excretion  of  carbon  during,  84 

excretion  of  nitrogen  during,  80,  82,  84 

experiments  on  dogs,  82 

experiments  on  man,  80,  84 

fat  as  source  of  energy  in,  81 

fuel  value  during,  86 

fuel  value  of  fat,  metabolized  during,  86 

metabolism  of  fat  during,  84 

nitrogen  excretion  during,  80,  82,  84 

origin  of  energy  in,  81 

proteid  as  source  of  energy  in,  81 

proteid  metabolism  during,  83 

relation  of  nitrogen  excretion  to  work  during,  125 

source  of  energy  for  work  during,  125 
Fat,  absorption,  43,  49 


INDEX  309 

Fat,  absorption  in  dogs  on  low  proteid  diet,  233,  261 
as  food,  6 
as  fuel,  6 

as  source  of  energy,  128 
as  source  of  energy  during  work,  58 
as  source  of  energy  in  fasting,  81 
composition  of,  6 
digestion  of,  in  intestine,  36 
digestion  of,  in  stomach,  36 
fuel  value  of,  15 

fuel  value  of,  metabolized  during  fasting,  86 
hydrolysis  of,  36 

influence  of  feeding,  on  body  fat,  44 
in  foodstuffs,  7 

laying  on  of,  from  overfeeding,  98,  99 
metabolism  during  fasting,  84,  86 
respiratory  quotient  of,  107 
saponification  of,  36 
specificity  of  body,  44 
synthesis  of,  43 

utilization  of,  in  dogs  on  low  proteid  diet,  261 
Fats,  availability  of,  13 

as  heat  producers,  58 
as  proteid  sparers,  92 
Fatty  degeneration,  270 
Fatigue,  relation  to  low  proteid  diet,  208 
Fenger,  S.,  293 

Fick  and  Wislicenus,  on  source  of  muscular  energy,  121 
Fischer,  Emil,  21 
Fisher,  Irving,  on  endurance  and  low  proteid  diet,  210 

on  method  of  indicating  food  values,  283 
Folin,  Otto,  theory  of  proteid  metabolism,  144 

Food,  absorption  and  utilization  of,  in  dogs  on  low  proteid  diet,  261,  262 
amounts,  required  for  proteid  needs  of  body,  274 
as  fuel,  6 

as  source  of  energy,  15 
availability  of,  12 
carbohydrates  as,  6 

character  of,  in  relation  to  bacterial  processes  in  intestine,  292 
consumption  and  obesity,  270 
consumption,  relation  to  prosperity,  160 
fats  as,  6 
fuel  value  of,  274 

of  fruitarians,  217 

in  experiments  on  proteid  requirement,  athletes,  198 

in  experiments  on  proteid  requirement,  professional 

men,  178,  180,  185 

in  experiments  on  proteid  requirement,  soldiers,  198 
of  Japanese,  219,  221 
fuel  value  requirement  of,  in  dogs,  234,  236,  245-255 


310  INDEX 

Food,  influence  of,  on  respiratory  quotient,  107 
needs  of  body  for,  169 
of  man,  2 
proteids  as,  3,  5 

real  need  of  body  for  proteid,  272 
relation  of  appetite  to,  162 
relation  of  nutritive  value  and  cost  of,  277 
requirements,  factors  modifying,  165 
temperance  in,  166,  168 
value  of  fruits  as,  290 
values  of,  method  of  indicating,  283 
Foods,  respiratory,  58 

time,  remain  in  stomach,  29,  30 
Foodstuffs,  carbohydrate  in,  7 
composition  of,  7 
fat  in,  7 
fuel  value  of,  7 
inorganic  salts  in,  7 
organic,  3 
plastic,  58 
proteid  in,  7 
water  in,  7 

Fritz,  photograph  of,  199 
Fruitarians,  dietary  of,  215 

fuel  value  of  food  of,  217 
proteid  consumption  of,  217 
Fruits,  value  of,  as  food,  290 
Fuel,  carbohydrate  as,  6 
fat  as,  6 
proteid  as,  6 
Fuel  value,  in  fasting,  86 

of  carbohydrate,  15 

of  fat,  15 

of  fat  metabolized  during  fasting,  86 

of  food,   in  experiments   on  proteid   requirement,   athletes, 

188 
of  food,  in  experiments  on  proteid  requirement,  professional 

men,  178,  180,  185 
of  food,   in   experiments    on  proteid    requirement,   soldiers, 

198 

of  food  of  fruitarians,  217 
of  food  of  Japanese,  219,  221 
of  foods,  274 
of  foodstuffs,  7 
of  proteid,  15 

of  proteid  metabolized  during  fasting,  86 
requirement  in  the  dog,  experiments  by  Munk,  234 
requirement  in  the  dog,  experiments  by  Rosenheim,  236 
requirement  in  the  dog,  experiments  by  Jagerroos,  236 
requirement  in  the  dog,  experiments  by  author,  245-255 


INDEX  311 


Gastric  digestion,  importance  of,  30 
object  of,  30 
products  of,  26 
Gastric  juice,  action  on  milk,  26 

composition  of,  25,  26 

functions  of,  25,  27 

hydrochloric  acid  in,  25,  26 

influence  of  diet  upon  flow  of,  25 

pepsin  in,  25 

psychical  stimulation  of,  24 
Gastric  secretion,  24 
Gelatin,  as  food,  4,  5 
Glassner,  see  Caspari  and  Glassner 
Gliadin,  cleavage  products  of,  70,  259 
Glutaminic  acid,  34,  67,  70,  259 
Glutenin,  cleavage  products  of,  259 
Glycerin,  36 
Glycocoll,  67 

Glycogen,  formation  from  proteid,  130 
in  liver,  46 

relation  to  sugar  of  blood,  46 
Growth,  influence  of  diet  on,  in  rats,  239 
Guanase,  71 
Guanin,  72 

H 

Habit,  in  dietetics,  159 

Heat,  furnished  by  fats  and  carbohydrates,  58 

production  during  sleep,  104,  105 

production  in  work,  110 
Herbivora,  bacterial  flora  in  intestine  of,  292 
Herter,  C.  A.,  on  bacterial  flora,  292 
Hirschfeld,  Felix,  on  minimum  proteid  requirement,  170 
Histidin,  34,  68,  70 

Hofmeister,  Franz,  on  sugar  assimilation,  47 
Hunt,  Reid,  on  low  proteid  diet  and  body  resistance,  226 
Hunter,  Andrew,  see  Watson  and  Hunter 
Hydrochloric  acid,  in  gastric  juice,  25,  26 
Hydrolysis,  of  fats,  36 
Hypoxanthin,  72 

I 

Indol,  37 

Inorganic  salts,  and  renal  activity,  298,  300 

in  foodstuffs,  7 

in  nutrition,  2 

relation  to  diet,  299,  300 


312  INDEX 

Intemperance  in  diet,  effects  of,  270 

Intermediary  metabolism,  see  Exogenous  metabolism 

Intestine,  absorption  in,  37 

chemical  changes  in,  33 

putrefaction  in,  37 

bacterial  flora  of,  292 
Invertase,  40 


Jagerroos,  B.  H.,  on  proteid  requirement  in  the  dog,  236 

Japanese  Army  and  Navy,  rations  of,  224 

Japanese,  dietary  of,  225 

fuel  value  of  food  of,  219,  221 
proteid  consumption  by,  219,  221 


K 

Katabolism,  50 

nature  of  proteid,  75 

oxygen  in,  62 

relation  to  intracellular  enzymes,  75 
Klemperer,  on  proteid  requirement,  171 


L 

Lactase,  40 

Lavoisier,  views  on  oxidation,  56 

Leucin,  34,  67,  70,  259 

Leucosin,  cleavage  products  of,  259 

Levulose,  assimilation  limits  of,  47 

Lewin,  see  Bergell  and  Lewin 

Liebig,  views  on  oxidation,  57,  120 

Lipase,  32 

Lipolysis,  by  pancreatic  juice,  36 

Liver,  function  of,  as  regulator  of  carbohydrate,  45 

glycogen  in,  46 

synthesis  of  proteid  by,  48 
Luxus  consumption,  of  proteid,  59 
Luthje,  101 

Lymphatics,  absorption  of  food  products  by,  44 
Lysin,  34,  68,  70,  259 

M 
Maltose,  21,  37 

behavior  when  introduced  into  blood,  39 
Man,  conservation  of  energy  in,  103 
energy  produced  by,  106 
experiments  on  oxygen  consumption  in,  126 
fasting  experiments  on,  80,  84 


INDEX  313 

Man,  food  of,  2 

metabolism  of  energy  in,  103 

minimum  proteid  requirement  in,  170,  171,  172,  174-208 
work  experiments  on,  110-116 
Mastication,  importance  of,  23 
Meat,  influence  on  growth  in  rats,  239 
Metabolic  changes  as  influencing  respiratory  quotient,  108 
Metabolism,  51 

and  old  age,  296 

endogenous,  145 

exogenous,  145 

Folin's  theory  of  proteid,  144 

influence  of  proteid  on,  83 

influence  of  carbohydrates  on  proteid,  92,  94,  95,  96,  97 

influence  of  fat  on  proteid,  92,  93,  96,  97 

influence  of  proteid  on  proteid,  88 

of  energy  in  man,  103 

of  fat  during  fasting,  84,  86 

oxidation  in,  60 

of  proteid  during  fasting,  83,  86 

Pfliiger's  theory  of  proteid,  138 

processes  of,  51 

significance  of  exogenous  and  endogenous  proteid,  49 

significance  of  proteid,  131 

Voit's  theory  of  proteid,  134 
Methyl  glycocoll,  see  Sarcosin 
Methyl  guanidin,  74 
Milk  sugar,  assimilation  limit  of,  47 

behavior  when  introduced  into  blood,  39 
utilization  of,  40 

Mineral  matter,  see  Inorganic  salts 
Minimum  proteid  requirement,  59 
Mixed  diet,  philosophy  of  a,  92,  276 
Monotony  of  diet,  influence  of,  242 
Morphotic  proteid,  134 

Munk,  Immanuel,  on  proteid  requirement  in  the  dog,  232 
Muscular  movements  of  stomach,  27-30 


N 

Needs  of  body  for  food,  169 
Nephritis,  in  relation  to  diet,  297 
Neumann,  R.  O.,  on  low  proteid  diet,  286 
Nitrogen,  distribution  of,  in  the  urine  in  relation  to  diet,  144 
needs  by  body,  4 

utilization  of,  in  dogs  on  low  proteid  diet,  262 
Nitrogen  excretion,  as  influenced  by  proteid,  59,  87,  90 
during  fasting,  80,  84 
during  work  in  fasting,  125 
during  excessive  work,  114,  127 


314  INDEX 

Nitrogen  excretion,  during  hard  work  on  proteid  diet,  123,  124 

in  experiments  on  proteid  requirement,  in  dogs,  245, 

249,  250,  251,  252,  255 
in  experiments  on  true  proteid  requirement,  athletes, 

187,  188 

in  experiments  on  true  proteid  requirement,  profes- 
sional men,  176,  177,  181,  185 
in  experiments  on  true  proteid  requirement,  soldiers, 

199,  200,  201 

relation  to  work,  122,  123,  124 
Nitrogen  equilibrium,  on  low  proteid  diet,  176,  177,  181,  188,  200,  201,  249, 

250,  251,  252,  255 
Nitrogen  requirement,  in  dogs,  234-236,  245-255 

in  man,  180,  184,  185,  187,  198,  227 
relation  to  body-weight,  184,  248 
Nitrogenous  equilibrium,  78 
Nitrogenous  metabolism,  theory  of  Folin,  144 
theory  of  Pfliiger,  138 
theory  of  Voit,  134 
Normal  diets,  155 
Nutrition,  factors  in,  16,  17 

influence  of  chemical  character  of  proteid  on,  256 
inorganic  salts,  as  aids  in,  2 
physiological  economy  in,  264 
purpose  of,  2 

Nutritive  balance,  as  affected  by  various  factors,  117,  118 
Nuclease,  71 
Nucleoproteid,  character  of,  3 

cleavage  products  of,  71 


Obesity,  relation  to  food  consumption,  270 

Old  age,  metabolism  in,  296 

Osborne  and  Clapp,  on  chemistry  of  proteids  of  wheat  kernel,  258 

Osmosis,  as  factor  in  absorption,  41 

Overeating,  evil  effects  of,  270 

Overfeeding,  in  laying  on  of  fat,  98,  99 

Oxidase,  xanthin,  73 

Oxidases,  64 

Oxidation,  in  metabolism,  60 

nature  of,  in  the  body,  60 

older  views  regarding,  52 

relation  to  enzymes,  75 

site  of,  in  the  body,  62 

value  of  respiratory  quotient  in  determination  of  substances 
undergoing,  125 

views  of  Lavoisier  on,  56 

views  of  Liebig  on,  57,  120 


INDEX  315 


Oxidative  cleavage,  61 
Oxygen,  in  katabolism,  62 

relation  to  decompositions  in  the  body,  61 
relation  to  proteid  decomposition,  59 
Oxygen  consumption,  in  climbing,  116 

in  relation  to  work,  123 
in  standing  at  rest,  116 
in  walking,  116 


Pancreatic  digestion,  of  proteids,  34 

products  of,  34,  67 
products  of,  of  strach,  37 
Pancreatic  juice,  composition  of,  32 

condition  of  trypsin  in,  33 
enzymes  in,  32 
secretion  of,  31,  32 
sodium  carbonate  in,  32 
Paths  of  absorption,  44 
Pawlow,  on  adaptation  of  saliva,  18 
Pepsin,  in  gastric  juice,  25,  26 
Peptones,  67 

absorption  of,  41 
cleavage  by  erepsin,  34 
effects  when  injected  into  blood,  41 
formed  in  gastric  digestion,  26 
Pfluger,  E.,  theory  of  proteid  metabolism,  138 

views  on  muscle  work,  123 
Phenol,  37 

Phloridzin  diabetes,  130 

Phosphorus,  excretion  of,  in  relation  to  work,  123 
Photograph,  of  athlete,  190 

of  Fritz,  199 
Photographs,  of  dogs,  248 

of  soldiers,  193 

Physical  endurance,  see  Endurance 
Physiological  economy  in  nutrition,  264 
Plastic  foodstuffs,  58 

Poisons,  relation  of  body  resistance  to,  on  low  proteid  diet,  226 
Polypeptid,  35 

Portal  vein,  absorption  of  food  products  by,  45 
Processes  of  metabolism,  51 

Products,  of  cleavage  of  wheat  kernel  proteids,  259 
of  gastric  digestion,  26 
of  pancreatic  digestion,  37,  67 
of  proteid  cleavage,  70 
of  putrefaction  in  intestine,  38 
of  salivary  digestion,  21 


316  INDEX 

Products  of  digestion,  absorption  of,  44 

Professional  men,  fuel  value  of  food  on  low  proteid  diet,  178,  180,  185 

nitrogen  equilibrium  of,  on  low  proteid  diet,  176,  177,  181 
true  proteid  requirement  of,  174 
Progeny,  influence  of  meat  diet  on,  in  rats,  240 
Prosperity,  relation  to  food  consumption,  160 
Proteid,  absorption  of,  in  dogs  on  low  proteid  diet,  233,  262 

absorption  of  cleavage  products,  47 

amounts  of  food  required  to  supply  needs  of  body  for,  272 

as  food,  3 

as  fuel,  6 

as  glycogen  former,  130 

as  source  of  energy,  122,  123,  124,  129 

as  source  of  energy,  in  fasting,  81 

availability  of,  12 

body-weight  on  diet  low  in,  170-175,  181,  185,  190,  199,  245,  249, 
250,  251 

carbon  moiety  of,  129 

chemical  basis  of  protoplasm,  51 

circulating,  134 

cleavage  products  of,  70 

composition  of,  3,  69 

consumption  by  fruitarians,  217 

consumption  by  Japanese,  219,  221 

decomposition  by  oxygen,  59 

decomposition  in  work,  58 

excessive  consumption  of,  relation  to  disease,  269 

effect  of  diet  exclusively  of,  on  rats,  239 

effect  on  dogs  of  diet  low  in,  233,  234,  237,  245-255 

fat  absorption  in  dogs  on  diet  low  in,  261 

food,  real  need  of  body  for,  272 

formation  of  carbohydrate  from,  129 

fuel  value  of,  15 

fuel  value  of,  metabolized  during  fasting,  86 

influence  of  chemical  character  of,  on  nutrition,  256 

diet  exclusively  of,  upon  progeny  of  rats,  240 
diet  low  in,  on  high  proteid  animals,  231,  233,  243 
on  excretion  of  nitrogen,  59,  87,  90 
on  metabolism,  83 
on  metabolism  of,  88 

in  foodstuffs,  7 

katabolism,  75 

luxus  consumption  of,  59 

metabolized  during  fasting,  86 

minimum  requirement,  59 

morphotic,  134 

need  of  body  for,  268 

nitrogen  equilibrium  on  diet  low  in,  176,  177,  181,  200,  201,  245, 
249,  250,  251,  252,  255 

overfeeding  with,  98 


INDEX  317 

Proteid,  reconstruction  of,  during  absorption,  42 

relation  of  endurance  to  diet  low  in,  210,  212 
relation  of  fatigue  to  diet  low  in,  208 
respiratory  quotient  of,  107 
resistance  of  body  to  poisons  on  diet  low  in,  226 
safety  in  relation  to  diet  low  in,  231 
significance  of  complete  cleavage  of,  35 
storing  of,  92,  98,  99,  100 
strength  tests  on  diet  low  in,  203,  206 
synthesis,  48,  49,  68 

utilization  of  fat  in  dogs  on  diet  low  in,  261 
utilization  of  nitrogen  in  dogs  on  diet  low  in,  262 
work  done  at  expense  of,  58 
Proteid  diet,  experiments  of  Neumann  on  low,  286 

body-weight  of  dogs  on  low,  245,  249,  250,  251 
body-weight  of  men  on  low,  170-175,  181,  185,  190,  199 
in  relation  to  nitrogen  excretion  during  hard  work,  123,  124 
vegetable  foods  in  relation  to,  291 

Proteid  metabolism,  influence  of  carbohydrate  on,  92,  94,  95,  96,  97 
influence  of  fat  on,  92,  93,  96,  97 
influence  of  proteid  on,  59,  87,  90 
Folin's  theory  of,  144 
Pflliger's  theory  of,  138 
significance  of,  131 
Voit's  theory  of,  134 
Proteid  requirement,  fuel  value  of  food  in  experiments  on,  athletes,  188 

fuel  value  of  food  in  experiments  on,  professional  men, 

178,  180,  185 

fuel  value  of  food  in  experiments  on,  soldiers,  198 
in  dogs,  experiments  of  Jagerroos,  236 
in  dogs,  experiments  of  Munk,  232 
in  dogs,  experiments  of  Rosenheim,  234 
in  dogs,  experiments  of  author,  243 
in  man,  169,  170,  171,  172,  174-202 
nitrogen  excretion  in  experiments  on,  athletes,  186, 

187,  188 
nitrogen  excretion  in  experiments  on,  in  dogs,  245, 

249,  250,  251,  252,  255 
nitrogen  excretion  in  experiments  on,  professional 

men,  177,  180,  185 
nitrogen  excretion  in  experiments  on,  soldiers,  197, 

200,  201 

relation  to  body-weight,  184,  188,  198,  227 
sample  diets  in  experiments  on,  178,  182,  189,  195 
Proteids,  as  tissue  formers,  58 

of  wheat  kernel,  cleavage  products  of,  259 
Proteoses,  26,  67,  69 

absorption  of,  41 

cleavage  by  erepsin,  34 

effects  when  injected  into  blood,  41 


318  INDEX 

Proteoses,  primary,  67,  69 

secondary,  67,  69 
Protoplasm,  51 
Protoproteose,  67,  69 
Ptyalin,  20 
Purin  bases,  71,  72 

relation  to  uric  acid,  73 
Putrefaction,  in  intestine,  37 
products  of,  38 


Rats,  effects  of  exclusive  proteid  diet  on,  239 
effects  of  rice  on,  240 
influence  of  meat  diet  on  progeny  of,  240 
Renal  activity,  and  diet,  297 

and  inorganic  salts,  298,  299,  300 
Rennin,  in  gastric  juice,  26 

Resistance  of  body  to  poisons,  relation  to  low  proteid  diet,  226 
Respiration  calorimeter,  102 
Respiratory  foods,  58 
Respiratory  quotient,  107 

influence  of  foods  on,  107,  126 

influence  of  metabolic  change  on,  108 

of  foodstuffs,  107 

relation  to  work,  125 

value  of,  in  determination  of  substances  oxidized, 

125 
Rest,  carbon  dioxide  output  during,  111 

influence  of,  on  oxygen  consumption,  126 
influence  of,  on  respiratory  quotient,  126 
Rice,  influence  of,  on  growth  in  rats,  240 
Rosenheim,  Theodor,  on  proteid  requirement  in  the  dog,  234 


S 

Safety  of  low  proteid  standards,  231 
Saliva,  adaptation  of,  18,  19 

function  of,  20 

psychical  secretion  of,  18 

secretion  of,  17,  18 
Salivary  digestion,  in  stomach,  23 
products  of,  21 
Salts,  see  Inorganic  salts 
Saponification  of  fats,  36 
Sarcosin,  74 
Schnyder,  115 

Scientific  research  and  typhoid  fever,  267 
Seasons  of  the  year,  relation  to  diet,  296 


INDEX  319 

Secretin,  32 

Secretion,  of  gastric  juice,  24 

of  pancreatic  juice,  31,  32 
of  saliva,  17,  18 

Sive"n,  on  proteid  requirement,  89 
Skatol,  37 

Sleep,  heat  production  during,  104,  105 
Soaps,  36 

Sodium  carbonate,  in  pancreatic  juice,  32 
Soldiers,  fuel  value  of  food  in  experiments  on  proteid  requirement  of,  198 

nitrogen  equilibrium  in  experiments  on  proteid  requirement  of, 
200,  201 

photographs  of,  193 

proteid  requirement  of,  192 

sample  diet  in  experiments  on  proteid  requirement  of,  195 

strength  tests  in  experiments  on  proteid  requirement  of,  203 
Specificity  of  body  fat,  44 
Standard  diets,  155 

Standing  at  rest,  oxygen  consumption  in,  116 
Starch  digestion,  products  of,  21,  37 
Steapsin,  36 
Stomach,  absorption  from  the,  31 

as  a  reservoir,  31 

digestion  in  the,  25-31 

fat  digestion  in  the,  36 

muscular  movements  of  the,  27-30 

salivary  digestion  in  the,  23 

time  foods  remain  in  the,  29,  30 
Storing  of  proteid,  92,  98,  99,  100 
Strength  tests,  on  low  proteid  diet,  athletes,  206 
on  low  proteid  diet,  soldiers,  203 
Sugar,  in  blood,  45 

in  blood,  relation  to  glycogen,  46 
Sugars,  behavior  when  introduced  into  blood,  39 

selective  action  in  absorption  of,  47 
Sulphur,  excretion  of,  relation  to  work,  123 
Synthesis,  of  fat,  43 

of  proteid,  48,  49,  68 


Temperance  in  diet,  166,  168,  270 

Tissue  formers,  58 

Tissue  metabolism,  see  Endogenous  metabolism 

Trypsin,  32 

condition  in  pancreatic  juice,  33 
Tryptophan,  67 

Typhoid  fever  and  scientific  research,  267 
Tyrosin,  34,  67,  70,  259 


320  INDEX 

U 

Underfeeding,  dangers  of,  214 
Urea,  74 

excretion  of,  influence  of  diet  on,  144 
relation  of,  to  creatin  and  creatinin,  74 
Uric  acid,  73 

excretion  of,  as  influenced  by  diet,  144 
relation  of,  to  xanthin  bases,  73 

Urine,  relation  of  diet  to  nitrogen  distribution  in  the,  144 
Utilization,  of  dextrose,  40 

of  disaccharides,  40 

of  fat  in  dogs  on  low  proteid  diet,  261 

of  nitrogen  in  dogs  on  low  proteid  diet,  262 


Variety  in  diet,  229,  242 
Vegetable  diet,  influence  upon  dogs,  254,  256 
Vegetable  foods,  relation  to  low  proteid  dietary,  291 
Vegetables,  cellulose  in,  influence  on  digestion,  263 
Voit,  Carl,  on  minimum  proteid  requirement,  171 
theory  of  proteid  metabolism,  59,  134 


W 

Walking,  oxygen  consumption  in,  116 

Water  in  foodstuffs,  7 

Watson  and  Hunter,  influence  of  diet  on  growth  in  rats,  239 

Wheat  kernel  proteids,  cleavage  products  of,  259 

Weight,  see  Body-weight 

Wislicenus,  see  Fick  and  Wislicenus 

Work,  carbon  dioxide  excretion  in  relation  to,  123 

carbon  dioxide  excretion  during,  111,  112 

due  to  proteid  decomposition,  58 

effect  of,  on  energy  exchange,  109,  110,  113,  115 

experiments  on  man,  110,  111,  112,  113,  114,  115,  116 

heat  production  in,  110 

influence  of,  on  oxygen  consumption,  126 

influence  of,  on  respiratory  quotient,  126 

nitrogen  excretion  during  excessive,  127 

nitrogen  excretion  during  fasting  in,  125 

proteid  decomposition  in,  58 

relation  of  diet  to,  126 

to  energy  exchange,  119 

fats  and  carbohydrates  to,  58 

nitrogen  excretion  on  proteid  diet  to  hard,  123,  124 

nitrogen  excretion  to  proteid  diet  to  hard,  122,  123,  124 


INDEX  321 


Work,  relation  of  oxygen  consumption  to,  123 
phosphorus  excretion  to,  123 
sulphur  excretion  to,  123 
respiratory  quotient  in  relation  to,  125 
source  of  energy  during  fasting  in,  125 
views  of  Argutinsky  on  muscle,  123 
views  of  Pfluger  on  muscle,  123 
views  of  Voit  on  muscle,  59,  134 


Xanthin,  72 
Xanthin  oxidase,  73 


577276 


3  1378  00577  2762 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


